All Tools

Mortgage calculator — monthly payment, total interest, amortization schedule, early payoff scenarios.

Loan comparison calculator — compare equal-payment vs equal-principal, multiple loans side by side, total interest breakdown.

Loan prepayment calculator — see how much interest you save by paying extra each month or one-time, with breakeven analysis.

Annuity & retirement calculator — see monthly income from your savings, accumulation + payout phases, multiple scenarios.

Compound interest calculator — see how money grows over time, with monthly contributions, charts, and breakdown.

Savings goal tracker — set a target (down payment, trip, emergency fund), see weekly/monthly contribution and projected date.

China personal income tax calculator — monthly, annual, with 5 insurance + 1 fund deductions.

China company income tax calculator — small/micro (2.5%/5%/25%) vs general taxpayer, R&D super-deduction, loss carry-forward 5 years.

China personal income tax special deduction simulator — 7 categories (kids/elder/mortgage/rent/education/medical/infant), year-end reconciliation included.

China vehicle purchase tax calculator — 10% rate on tax-exclusive price, with NEV exemption rules, plus on-road cost breakdown.

China second-hand house transaction tax calculator — contract tax + VAT + personal income tax + agency fee + transfer fee, by city + house tenure + family situation.

Property fee calculator — calculate Chinese residential management fees, garage, heating, elevator, with regional rate references.

Currency converter — 50+ currencies with offline reference rates, convert without internet, source data updated each release.

Expense tracker — log spend, categorize, see monthly totals, all in your browser.

Wedding budget planner — itemized cost calculator with regional benchmarks for venue, photography, catering, etc.

Kids allowance calculator — age-appropriate weekly/monthly amount with chore-based breakdown, savings goal sandbox.

Tip & split calculator — calculate tip by percentage, split bill among friends, round-up options, multi-currency.

Meeting cost calculator — see how much that meeting is costing in real-time, with team salary data and overhead multiplier.

Car loan calculator with prepayment — bank vs 4S dealer financing comparison, equal-installment / equal-principal / balloon plans, prepayment-savings simulation.

Estimate daily and monthly LLM spend from tokens, request volume, and editable model prices.

China housing-provident-fund loan calculator — single + dual contributor max loan, monthly payment (equal-principal + equal-installment), top-30 cities 2025 caps.

China pension calculator — basic + personal-account + transitional pension formulas (2024 reform), by province average wage, contribution years, base, with 2055 projection.

China used-car price estimator — depreciation curve by brand tier + age + mileage + condition, plus 4S trade-in vs private vs auction net comparison.

China unemployment benefits calculator — monthly amount + total months by city + insurance years, per 2026 policy.

China overtime pay calculator — workday 1.5×, weekend 2×, statutory holiday 3× per Labor Law Art. 44, with 31 provincial minimum-wage tables.

Convert nominal APR to effective APY (and back) at any compounding frequency — daily, monthly, quarterly, or continuous. Two-way, instant, browser-only.

Price any fixed-coupon bond from face value, coupon rate, YTM and maturity. Shows premium / discount / par, current yield, and the coupon-vs-face split. 100% in your browser.

How many units must you sell to stop losing money? Enter fixed costs, price, and variable cost per unit for break-even units, break-even revenue, and contribution margin — browser-only

Find the compound annual growth rate between any two values — plus reverse-solve the end value or the years, and see simple vs annualized side by side, browser-only

NOI ÷ property value × 100 = cap rate — solve for rate, value or NOI, with gross rent multiplier — browser-only

Cap cost, residual, money factor, term → exact monthly payment with depreciation + finance + tax breakdown — 100% in your browser

Certificate of Deposit maturity, interest & effective APY — APY or APR + compounding, early-withdrawal penalty, CD ladder — browser-only

Churned ÷ starting customers = churn % — retention, monthly→annual, average lifetime, optional MRR churn — browser-only

Work out sales commission three ways — flat rate, progressive tiers, or reverse-solve the sales you need to hit an income target. Browser-only, shareable.

Conversions / visitors, solve for any of the three, plus A/B uplift and visitors needed for a goal. Browser only.

CPM = ad spend ÷ impressions × 1000 — solve for spend, impressions or CPM, plus CPC, CTR and CPA off the same budget — browser-only

Net profit, ROI%, fees, and the break-even sell price for a crypto trade — enter by quantity or by amount invested, both buy and sell fees counted — browser-only

CLV / LTV for SaaS and e-commerce — simple and SaaS formulas, LTV:CAC health check, one-click copy — runs in your browser

Snowball vs avalanche — payoff date, total interest, and what an extra payment saves — browser-only

Total monthly debt ÷ gross monthly income, with front-end and back-end DTI, lender bands and one-click copy, all in your browser

Straight-line, double declining balance and sum-of-years-digits — full year-by-year depreciation schedule with book value — browser-only

Sale price, amount saved, % off — plus stacked discounts, BOGO, spend-X-save-Y, tax, and reverse % — instant, browser-only

Share price + annual dividend → yield %, annual/quarterly/monthly income, and yield on cost after years of dividend growth — browser-only

Pick a date and a fiscal-year start month — get the FY label, quarter, day count and exact start/end dates, browser-only

Back into the hourly rate you must charge from your target salary, business expenses, billable hours, profit margin, and taxes — browser-only

Project the future value of a lump sum plus regular contributions — full time-value-of-money math, year-by-year, browser-only

Income + debt + down payment + rate → the max home price a lender's 28/36 rule will actually approve — browser-only

See what your money is really worth — future value, purchasing power, and the rule-of-72 halving point, all from one inflation rate

COGS ÷ average inventory = turnover ratio, plus days sales of inventory (DSI) — type the average directly or let beginning + ending fill it in — browser-only

Cost ⇄ price ⇄ markup % ⇄ margin % — solve any two, see both rates side by side — 100% in your browser

Add up assets, subtract debts, see your real net worth — with a debt-to-asset ratio and composition bars, all computed in your browser

Discount every cash flow back to today — net present value, IRR, payback period, per-period present value — browser-only

Stripe, PayPal, Square fees — see what lands in your account, and gross-up to net any target — 100% in your browser

Convert story points to hours, days and sprint capacity from your team's velocity profile — made for roadmap and sprint planning conversations.

Discount a future sum or a level annuity back to today — PV = FV / (1 + r)^n, single sum or annuity, browser-only

How much rent can you actually afford? 30% rule, landlord 3× gate, and a debt-aware 50/30/20 number — all client-side

See whether buying beats renting and investing the difference — net cost, terminal equity, and the break-even year, all in your browser

Project your retirement pot from age, savings, monthly contributions, return and inflation — with a 4% safe-withdrawal income, growth curve, and goal-gap check. Browser-only.

ROI %, net gain, annualized ROI (CAGR) and payback period — one screen, share a link — 100% in your browser

Estimate doubling time from a rate (72 ÷ r), or the rate from a target time — side by side with the exact ln(2)/ln(1+r) figure — browser-only

Turn a raise into real numbers — new salary by year/month/hour, dollar increase, and the inflation-adjusted raise that tells you if you actually came out ahead

Hourly ⇄ daily ⇄ weekly ⇄ monthly ⇄ annual pay — set your hours/week and weeks/year, see all five at once — browser-only

Add or remove US sales tax — split state + local rates, real 2024 state base rates on tap, browser-only

I = P × r × t — solve for interest, principal, rate, or time, plus total and a simple-vs-compound gap — browser-only

Cash in bank ÷ burn rate = months left. Enter balance, monthly spend, and revenue (with optional growth) for runway, cash-out date, and the date you must start fundraising — browser-only

Team velocity + sprint length + team size → what 13 story points actually means in hours, days and sprints — both directions, browser-only.

Gross → net pay, any country — your own tax rate, pre-tax & post-tax deductions, reverse-solve — browser-only

Weekly time card — clock in/out + lunch → daily hours, weekly total, gross pay, 40h overtime — browser-only

Add tax, remove tax, or find the rate — net ⇄ gross at any VAT / GST / sales-tax rate — instant, browser-only

Body Mass Index calculator with WHO + Asian classifications — metric and imperial — browser-only

BMR calculator — basal metabolic rate by Mifflin-St Jeor and Harris-Benedict (compared side-by-side).

Calorie calculator — daily calorie needs (BMR + TDEE), weight loss/gain targets, macro breakdown.

Body fat % calculator — 4 formulas (US Navy / BMI-based / YMCA / Jackson-Pollock) with body shape visualization.

Water intake calculator — daily water target by body weight, activity, climate. With drink-log to track today's progress.

Protein intake calculator — daily grams by body weight, activity, goal (cut/maintain/bulk), per ISSN 2017 guidelines.

Macro nutrient calculator — TDEE + protein/fat/carb split for cut/maintain/bulk goals, with 3 split presets (high-protein/keto/balanced) and meal example.

Intermittent fasting tracker — 16:8 / 18:6 / 20:4 / OMAD / 5:2 / 36h timer with stages and history log.

Weight loss tracker — set target, log daily weight, see trend, project goal date with real calorie math.

Weight training tracker — log compound lifts (squat/bench/deadlift/OHP), track 1RM via Epley formula, see strength gains by week.

Strength 1RM calculator + training program — 6 formulas (Epley/Brzycki/Lombardi/O'Conner/Lander/Mayhew), %1RM table, Wendler 5/3/1 + Sheiko + Madcow templates.

Heart rate zones calculator — max HR (4 formulas) + 5 training zones (recovery/aerobic/tempo/threshold/VO2max), with workout examples.

Stair climbing calorie calculator — calculate kcal burned by floors climbed, with METs-based formula.

Running pace calculator — convert between pace / time / distance, predict 5K/10K/half/full marathon from one race.

Marathon time predictor — input 5k/10k/half time, get full marathon prediction via 3 formulas (Riegel/Cameron/VDOT), with pace zones and weekly mileage advice.

Sleep cycle calculator — 90-minute REM cycles. Find best bedtime if you must wake at X, or best wake time if you sleep at Y.

Sleep debt calculator — track this week's sleep hours, see your accumulated debt, get a realistic recovery plan based on research.

Ovulation & fertility tracker — predict next 6 months of fertile windows, track BBT, find best conception days.

Period & ovulation calculator — predict next period, fertile window, safe days (based on calendar method).

Pregnancy due date calculator — track weeks, trimester, baby development by week.

China maternity benefits calculator — leave days by province (98 base + extension 30-180 days), maternity allowance (avg-wage × leave-days / 30), medical reimbursement, 2025 policy.

Child adult-height predictor — 3 scientific methods (mid-parental / Khamis-Roche / CDC growth percentile), with confidence range + growth chart.

China 0-6y child immunization schedule — 11 free + 12 paid vaccines, generates personalized calendar from baby's birthdate, with per-dose reminders.

A1C ⇄ estimated average glucose, both ways, mg/dL or mmol/L, with the ADA range — educational, browser-only

Widmark-formula BAC estimate from drinks, body weight, sex and time — educational only, never a fit-to-drive verdict — browser-only

Enter systolic and diastolic, see your AHA category on a color scale — Normal to Crisis, education only, runs in your browser

Four formulas side by side — Mosteller, DuBois, Haycock, Gehan-George — cm/kg or in/lb, one-click copy, browser-only

Track how much caffeine is still in your system, how much is left at bedtime, and when it drops to a sleep-friendly level — half-life model, browser-only.

Pick a daily calorie deficit, enter your current and goal weight, and see how many weeks it takes and the date you'd hit your target — with a safety check, browser-only

MET-based calorie burn for 30+ activities — running, cycling, swimming, HIIT, housework — stack and total — browser-only

20-min power × 0.95 = FTP — Coggan 7 power zones, watts and W/kg, one-click copy — runs in your browser

Fat-Free Mass Index from weight, body-fat and height, with normalized FFMI and the natural-limit bands, 100% in your browser

Devine + Robinson + Miller + Hamwi formulas, side by side, plus the healthy BMI weight band — metric and imperial — browser-only

Estimate how many days jet lag will last and build a day-by-day plan to pre-shift your body clock before you fly — eastbound vs westbound, light and melatonin timing, all in your browser

Boer, James and Hume LBM side by side, plus fat mass and a direct body-fat path, metric or imperial, fully in your browser

Estimate your 1RM from any set with five formulas at once, then read a full %1RM training-load table — kg or lb, browser-only

Target weight → exactly which plates to slide on each end — kg & lb, with a live barbell diagram — browser-only

Pre-pregnancy BMI + week → IOM recommended total gain, the by-week target, and an on-track check — singleton & twins — browser-only

Steps ⇄ distance from your stride: type a stride or estimate it from height, see km or miles, and find how far 10,000 steps go — browser-only

Solve any one of pace, time, or distance from the other two, with per-100 splits, pool-length lap time, and metre to yard conversion, all in your browser

TDEE calculator — BMR × activity factor, with cut/bulk calorie targets and projected weekly weight change.

Estimate your maximal oxygen uptake from four field tests — Cooper run, 1.5-mile, resting HR, Rockport walk — with a fitness grade by age and sex

WHtR = waist ÷ height, one number that flags abdominal fat better than BMI, with cm/in, sex-aware bands and one-click copy, browser-only

WHR = waist ÷ hip, scored against the WHO health-risk bands by sex, with an optional waist-to-height check — runs entirely in your browser

Normalise a powerlifting total across bodyweights with the classic 1994 Wilks coefficient — kg or lb, instant score, browser-only

Calculate your exact age — years, months, days, hours. Compare two dates or count to a future date.

Days / weeks / months / years between two dates — plus business-days mode — browser-only

Countdown timer — to any date and event, with live ticking down to seconds.

Work tenure calculator — service years, annual leave entitlement (China), retirement countdown.

Convert any time between any two timezones — DST-aware, IANA database — browser-only

Plan meetings across timezones — see when everyone's working hours overlap.

Cooking unit converter — tsp / tbsp / cup / oz / ml / g for 100+ common ingredients with density.

Recipe scaler — paste any recipe, change servings, get all ingredient amounts auto-scaled. Handles fractions and unit conversion.

Fish tank size calculator — input fish species and count, get the minimum tank gallons/liters needed and stocking density warnings.

Pet age calculator — accurate dog/cat human-age equivalent, with breed size adjustment, lifespan stages.

Pet food calculator — RER + activity factor for dogs and cats, exact daily grams based on weight, age, neuter status, and kibble kcal/100g.

Screen time budget — track and visualize daily screen time across phone/tablet/PC, with age-based recommendations from WHO/AAP.

BPM tap counter — tap the spacebar to the beat, instantly get tempo with running average, find your song's tempo for DJ / dance / metronome.

Typing speed test — WPM, accuracy, real-time mistakes, English + Chinese pinyin modes.

Airline luggage allowance — 50+ carriers' carry-on / checked baggage rules with size, weight, and excess fee.

China drunk-driving penalty reference — BAC threshold (20/80), license suspension/revocation, criminal charges, insurance impact, by scenario.

China three-child birth subsidy policy finder — per province / city one-time + monthly + housing + education subsidies (2024-2025 latest).

Pomodoro timer — 25/5 classic, plus 50/10 and 90/15 long-focus modes, with sound, browser tab title, daily stats.

Add or subtract days, weeks, months, and years from any date — plus a business-day mode that skips weekends. Runs entirely in your browser.

The exact gap between two birthdays — years/months/days, percentage, and the date one person is twice the other's age — browser-only

Flour = 100%. Read hydration, salt and yeast as percentages, or scale a recipe to any flour weight — browser-only

AVG, OBP, SLG and OPS from one stat line — three-decimal display like .300, walks kept out of at bats — browser-only

Thickness × width × length ÷ 12 = board feet — multi-row cut list, per-BF cost, imperial ⇄ m³ — browser-only

Room area × ceiling × orientation × people → cooling BTU/h, 匹 (horsepower) and kW — sizes an AC right the first time — browser-only.

Working days between two dates, or a date N working days out — weekends + holidays excluded, browser-only

Volume × fill rate × wax density = grams of wax, plus fragrance oil at your load percent — soy, paraffin, beeswax, mL or fl oz — browser-only

Rooms + roll width + waste → linear metres, billed area (m² / ft² / sq yard) and cost — browser-only

US ⇄ UK ⇄ EU ⇄ CN ⇄ S–XXL for men & women — tops, trousers, dresses, suits — with the body measurements behind every size — browser-only

Coffee-to-water ratio calculator — type 1:16, pick a brew method, get exact grams of coffee and water for any batch

Slab, column, round footing & stairs → cubic meters/yards + cement bags, sand and gravel — browser-only

Type any date and read the weekday back — works for 1066, 1900 or 3000, with day-of-year, ISO week and days-from-today

How many days until a date — plus weeks, months, business days, exact remaining, and the weekday it lands on

Air temperature + relative humidity to the exact dew point, with a comfort band — Magnus formula, reversible, browser-only

How long to download a file at a given speed, plus reverse-solve the bandwidth a deadline needs, with the 8-bits-per-byte trap handled, browser-only

Wall + ceiling area → sheets, drywall screws, joint tape & compound — metric and imperial — browser-only

Seconds ⇄ minutes ⇄ hours ⇄ days ⇄ weeks, plus human-readable, ISO 8601 duration and HH:MM:SS — one input, every format — browser-only

Power × hours × tariff → kWh and cost per day, month, and year — add multiple appliances, account for standby — browser-only.

Battery kWh + charge % + tariff → cost per charge, per 100km/mile, and how much you save vs petrol — browser-only

Total run + post spacing → posts, panels/pickets, rails, concrete bags — metric & imperial — browser-only

Measure your wood pile, get cords + face cords, compare price per cord — feet ⇄ metres, one-click copy, browser-only

Room sizes + flooring type + box coverage + waste → net area, boxes, planks, and cost — metric or imperial, browser-only.

Trip fuel cost from distance + economy + price — round trip, per-person split, L/100km ⇄ MPG — browser-only.

Score differential and WHS Handicap Index from your rounds, best-N averaged ×0.96, single-round quick mode, one-click copy, browser-only

Lawn area + species + new/overseed → exact seed weight and bag count — metric & US — browser-only

Area + depth → volume, tonnes, bulk bags — driveways, drainage, paths — browser-only

Air temperature + humidity to the real "feels-like" temperature, with NWS risk level — exact Rothfusz regression, browser-only

Stack wall and roof layers, get total R-value, U-value and metric RSI — glass wool, foam board, wood and more — browser-only

Kills ÷ deaths, plus KDA with assists and the kills you need to hit a target K/D — browser-only, share-by-link

Is it a leap year? Type any year for a yes/no, the 4/100/400 rule worked out, Feb length, and the next leap year, browser-only

Pick a meat and a doneness, get the internal cooking temperature in °F and °C, with the USDA safe minimum and the chef target side by side

Pick any date, see the moon phase, illumination percentage and moon age, plus this month's principal phases, all in your browser

Distance + fuel → MPG (US/UK), L/100km, km/L, all at once + cost per mile/km — browser-only

Garden bed area + spread depth → cubic yards, bags and bulk — multi-bed, metric/imperial — browser-only

Decimal, fractional and American odds with implied probability, all four update live as you type

Wall area → litres & cans of paint, with doors/windows deducted, coats and price — metric & US units, browser-only

NFL quarterback passer rating from completions, attempts, yards, TDs and INTs — with the NCAA college formula and a perfect-158.3 check — browser only

Area ÷ paver size, rounded up, +10% for cuts — pavers per ft²/m², total cost, ft+in or m+cm — browser-only

Baker's percentage pizza dough — flour, water, salt, yeast, oil by weight — browser-only

Bed size + in-row & row spacing → exact plant count — square vs triangular layout — browser-only

Find how many gallons (and liters and cubic meters) your pool holds — rectangle, round, oval, or sloped floor — in feet or meters

US ⇄ UK ⇄ EU ⇄ JP ⇄ CN ⇄ inner circumference & diameter (mm) — type any one, get every size at once — browser-only

Convert roof pitch between rise-over-run, degrees and percent, plus the rafter multiplier and real rafter length — browser-only

Roof footprint + pitch → real sloped area, roofing squares, shingle bundles or sheets and underlayment rolls — metric & US, browser-only

US ⇄ UK ⇄ EU ⇄ CN ⇄ JP + foot length (cm/in) — men, women, kids — browser-only

Add every room, get one total in ft² and m² at once — waste % + cost — browser-only

Total rise + steps → rise/run, slope, Blondel comfort check + side-view diagram — metric & imperial, browser-only

Room area + tile size + grout joint + waste → tiles, boxes, and cost — metric or imperial, browser-only.

Hours between two times, add or subtract time, and add up a timesheet — decimal hours + pay — browser-only

Tip percent, grand total, per-person share, pre-tax or post-tax, round-up split, browser-only

Decode 225/45R17 into diameter, sidewall, circumference & revs/km — then compare two tires for speedometer error and clearance change. Browser-only.

Split group trip, dinner & shared-flat costs — track who paid what, who joined which expense, and get the fewest transfers to settle up. 100% in your browser.

Compare price per 100 g, per litre or per piece across packs — normalize g⇄kg and mL⇄L, flag the cheapest, copy the result — browser-only

Wall size + roll spec + pattern repeat → strips per roll, total strips, rolls to buy — handles straight & half-drop match — browser-only

What week number is today? ISO 8601 (Mon-start) + US (Sun-start), plus year + week → date range — browser-only

Rise → ADA 1:12 ramp length, slope percent, angle and a pass/fail check — reverse mode too — browser-only

Wins ÷ total games × 100% with draws, plus the win streak you need to hit a target rate and how many losses you can afford, browser-only

Turn air temperature and wind speed into a feels-like number — and a frostbite warning — using the official NWS / Environment Canada formula. Metric or imperial, browser-only.

Scientific calculator — sin / cos / log / sqrt / power, with full keyboard input + history, deg/rad mode.

Convert between length, weight, temperature, area, volume, speed, time — instant, browser-only

5 common percentage calculations — "x% of y", "x is what% of y", percentage change, increase/decrease — instant, browser-only

Generate cryptographically-secure random integers — single or batch, with/without duplicates — browser-only

Math formula reference — algebra, geometry, trigonometry, calculus, statistics, all in one place.

Interactive periodic table — 118 elements, properties, electron config, search.

Birthday paradox calculator — see the probability of shared birthdays in a group of N people, visualized step by step.

Calculate aspect ratio — fix any 1 of [width, height, ratio], get the other two.

Number base converter — binary, octal, decimal, hex, and any base 2-36. Bitwise too.

Complex number calculator — +-×÷ + conjugate + modulus + argument + polar/Cartesian conversion + powers + roots + Euler form, complex plane visualization.

Matrix calculator — add/sub/multiply/inverse/determinant/transpose/rank/RREF/eigenvalues for n×m matrices, step-by-step.

Quadratic equation solver — ax² + bx + c = 0, discriminant analysis, real + complex roots, vertex/intercepts, parabola visualization.

Trigonometry calculator — sin/cos/tan + inverse + sec/csc/cot, degree/radian/gradient, unit circle visualization, exact values.

Derivative calculator with step-by-step — symbolic differentiation, chain/product/quotient rule shown, plot f(x) and f'(x).

Indefinite integral calculator step-by-step — symbolic integration, substitution + integration by parts shown, plot f(x) and F(x).

Basic statistics calculator — mean/median/mode/variance/std-dev/quartiles/range/IQR/skewness/kurtosis + histogram + box plot, paste any numbers.

Probability distribution visualizer — normal/t/chi-sq/F/binomial/poisson/exp/uniform PDF+CDF, P(a≤X≤b) area, z/p table replacement.

Chemistry equation balancer — paste an unbalanced equation, solve coefficients using the matrix method, show step-by-step.

Linux permission (chmod) calculator — convert between octal (755), symbolic (rwxr-xr-x), and ls -l forms, with safety warnings.

CSS px ↔ rem ↔ em converter — visual scale, base font size adjustable.

Unix timestamp ⇄ human date — seconds / milliseconds / ISO 8601 — UTC and local — browser-only

IELTS band calculator — convert listening/reading raw scores to band, average four skills, see your overall band.

MBTI quick test — 28 questions, 5 minutes, get your 4-letter type with detailed reading.

College major matcher — Holland code (RIASEC) test, 40 questions, recommend 10+ matching majors with career path.

China gaokao major recommender 2026 — filter by score range + subject combo (3+1+2) + interest + employment outlook, 150+ undergrad majors across 12 disciplines.

Astable f = 1.44/((R1+2R2)C) + monostable t = 1.1RC — pick R1, R2, C in Ω/kΩ and µF/nF, read frequency, duty cycle and pulse width — browser-only

Area between two concentric circles — A = π(R² − r²), ring width, inner and outer circumference, solve backwards from area — browser-only

Frequency in MHz to dipole, quarter-wave and full-wave length, with velocity factor, in metres or feet, browser-only

Arithmetic sequence calculator — nth term, sum of the first n terms, and the common difference from any two terms, all in your browser.

Test if a number equals the sum of its digits each raised to the digit count (153 = 1^3 + 5^3 + 3^3), with full breakdown and a range list. Browser-only.

product molar mass ÷ Σ reactant molar masses × 100 — green-chemistry atom efficiency, with how it differs from percent yield — browser-only

Capacity ÷ load × efficiency = runtime — mAh and Wh modes, reverse-solve capacity, charge time, share link — browser-only

Driven speed N2 = N1 × D1 / D2, solve any unknown, plus belt speed and drive ratio, browser-only

Expand (a + b)ⁿ term by term with exact BigInt coefficients, substitute numbers like (2x + 3)⁴, and pull out any single term — browser-only

F = ρ·V·g · Archimedes' principle · will it float or sink · fresh/sea water + air presets · apparent weight · 100% browser-only

Read a 3-digit capacitor code both ways: 104 to 100 nF, or a value back to its code, with pF / nF / µF and tolerance letters, browser-only

E = ½CV² stored energy + charge Q = CV — solve any one of C, V, E from the other two — browser-only

Solve F = m·v²/r for force, mass, speed or radius, with angular speed ω and centripetal acceleration, browser-only

Know any one of radius, diameter, circumference or area, get the other three, plus arc length and sector area, browser-only

Spindle RPM + feed rate from tool diameter, cutting speed, flutes and chip load — imperial ⇄ metric, material reference, one-click copy — browser-only

nPr, nCr, n!, n^r and combinations-with-repetition — exact BigInt results with the formula and worked steps — browser-only

P1V1/T1 = P2V2/T2 solver, find any one of the six gas quantities, with Boyle, Charles and Gay-Lussac special cases, browser-only

Turn ax² + bx + c into vertex form a(x − h)² + k with every step shown — vertex, axis of symmetry, min/max, and solved by completing the square — browser-only

Static compression ratio from swept + clearance volume, or from bore, stroke, chamber, dome and gasket — cc or ci — browser-only

Radius + height of a right circular cone, instant volume ⅓πr²h, slant height, lateral and total surface area, plus reverse-solve, browser-only

Mean and proportion confidence intervals with margin of error, exact z critical values, one-click copy, browser-only

Expand a decimal or fraction into a continued fraction [a0;a1,a2,...] with the convergents that best approximate it — browser-only

Great-circle distance between two lat/long points with the Haversine formula, plus bearing and midpoint, all in your browser

Paste X,Y pairs → Pearson r, r², covariance, regression line and a scatter plot — runs entirely in your browser

F = k·q1·q2 / r² — solve electrostatic force, distance or charge, signed result, µC/nC units, scientific notation — browser-only

Volume, surface area and capacity of a cylinder from radius or diameter and height — reverse-solve for height, see litres of water — browser-only

Add sound levels, convert ratio ⇄ dB (power 10·log, amplitude 20·log), and read a common-sound reference table — browser-only

Solve ρ = m / V for density, mass, or volume · mixed units (g, kg, lb, mL, L, cm³, gallon) · 20 substance presets · floats-or-sinks verdict — all browser-only

Near limit, far limit, total depth of field & hyperfocal distance from your sensor, focal length, aperture and focus distance — browser-only

Subfactorial !n — the number of permutations where nothing stays in its own place, exact via BigInt, with the 1/e probability — browser-only

Exact odds for any NdS roll: full sum distribution, expected value, and P(sum = / ≥ / ≤ X), counted not simulated

Solve C1V1 = C2V2 and ratio dilutions (1:10) — stock + water amounts in mL / L / fl oz / gal — browser-only

List every factor of a number — divisor count, sum of divisors, factor pairs, prime and perfect-number check — runs in your browser

Exact n!! computed on BigInt — the full expansion (7!! = 7×5×3×1 = 105), odd or even chain, and the bridge to the ordinary factorial, all in your browser

Turn any proper fraction into a sum of distinct unit fractions with the Fibonacci-Sylvester greedy algorithm, with the steps shown, browser-only

v = √(2GM/r) — escape + orbital velocity for any planet, moon or star, in m/s, km/s and mph — browser-only

E[X] = Σ x·p — enter outcomes and probabilities, get expected value, variance and standard deviation, all in your browser

EV = log2(N²/t) from aperture + shutter + ISO, plus equivalent-exposure solving and a Sunny-16 reference — browser-only

Current grade + final weight + target → exactly what you need on the final — browser-only

Add, subtract, multiply, divide fractions — auto-reduced, with steps, mixed ⇄ improper ⇄ decimal — browser-only

h = ½gt² · v = √(2gh) · solve from height, time, or impact speed · Earth, Moon, Mars gravity · browser-only

Convert frequency to wavelength and back with λ = v/f, pick the wave speed, read the EM spectrum band, copy in one click, browser-only

Conical frustum (truncated cone) volume, slant height, lateral and total surface area from R1, R2 and h — browser-only, one-click copy

Paste a DNA or RNA sequence and get GC%, AT%, per-base counts, length and a melting-temperature estimate. FASTA headers and spaces are ignored, invalid bases flagged, all in your browser.

GCD + LCM of any list of integers — Euclidean steps, prime factorization, prime-factor table — exact BigInt math, browser-only

Gear & transmission ratio plus bicycle gear inches, development and speed from cadence — exact, browser-only

Geometric sequence calculator — nth term, sum of first n terms, and infinite series sum from first term a and common ratio r, all in your browser.

Split any length by φ = 1.618 — long/short segments, golden sequence, font scale, layout columns, golden rectangle — browser-only

Weighted GPA from courses + credits + grades — US 4.0 / 4.3 and China 4.0 / 4.5 conversion, letter ⇄ percentage ⇄ point — browser-only

Weighted course grade + what you need on the final — multi-row categories, letter grade, shareable link — browser-only

F = G·m1·m2 / r² · solve for force, distance or mass · scientific notation · Earth/Moon/Sun presets · 100% browser-only

Solve any radioactive-decay unknown — initial amount, remaining amount, elapsed time, or half-life — with exact exponential math, all in your browser

Replace N with the sum of its squared digits — reach 1 and it is happy, hit the 4-cycle and it is not. See every step.

Buffer pH = pKa + log([A⁻]/[HA]) — forward and reverse, acetate/phosphate/Tris/bicarbonate presets — browser-only

F = k·x spring calculator: solve any one of force, spring constant or displacement from the other two, plus elastic potential energy ½kx² — browser-only

Solve any one of horsepower, torque or RPM from the other two — HP = T × RPM / 5252, HP↔kW and lb·ft↔N·m built in — browser-only

Solve PV = nRT for pressure, volume, amount, or temperature — pick any unknown, mix any units, runs in your browser

KE = ½mv², solve for energy, mass or speed, with formula steps and momentum, all in your browser

f = 1 / (2π·√(L·C)) — frequency from L and C, or solve back for the capacitor or inductor — angular frequency, one-click copy, browser-only

R =(Vs − n·Vf)/ If, with nearest E12/E24 value, resistor wattage and a dark-LED check, browser-only

W/m × length = total watts · watts ÷ volts = amps · +20% headroom sizes the supply · 5V / 12V / 24V · browser-only

Solve 1/f = 1/do + 1/di — enter any two of focal length, object and image distance, get the third plus magnification and a real/virtual verdict, browser-only

log_b(x), ln, log₁₀, log₂ and antilog in one place — change-of-base steps shown, one-click copy, browser-only

RC and LC filter −3 dB cutoff frequency · fc = 1/(2πRC) · reverse-solve the capacitor or resistor · browser-only

Width × height → megapixels, aspect ratio, file size, and max print size at any DPI. Reverse it too. 100% in your browser.

a mod n in both conventions — the % your language returns AND the math mod that is never negative, plus floor quotient, modular power and inverse

Molal concentration b = n / m — moles of solute per kilogram of solvent, solve any one of moles, solvent mass, or molality, or start from grams + molar mass, browser-only

Type any chemical formula — get molar mass, a per-element mass-percent table, and mass↔mole conversion. IUPAC weights, browser-only.

Molar concentration c = n / V — solve any one of moles, volume, concentration, or go straight from grams + molar mass — browser-only

Pick a shape, enter mass and size, read I in kg·m² — cylinder, sphere, rod, point mass, plus rotational KE — browser-only

p = m·v and J = F·Δt = Δp — solve any one of momentum, mass, velocity, impulse, force or time, with kg·m/s, g, m/s and km/h units — browser-only

n! / (k1!·k2!·…) computed exactly with BigInt — ways to split n items into fixed-size groups, the multinomial-theorem term coefficient, browser-only

Two notes in, the interval out: name, semitones, frequency ratio and cents, plus a reverse build from root plus interval

Note name ⇄ frequency (Hz) — A4 = 440/432/442, MIDI number, cents off — browser-only

One number in, every format out: thousands grouping, currency, percent, scientific, engineering, compact (K/M/万), ordinal, byte size — plus reverse parsing. 100% browser-only.

Enter any two of voltage, current, resistance, or power — get the other two plus the formula used — with mV/V/kV, µA/mA/A, Ω/kΩ/MΩ, mW/W/kW prefixes — browser-only.

Inverting −Rf/Rin and non-inverting 1+Rf/Rin gain, in V/V and dB, with output voltage and a reverse resistor solver, browser-only

T = 2π·√(a³ / GM) · Kepler's third law · solve period or semi-major axis · orbital speed · Sun/Earth/Jupiter presets · 100% browser-only

Add resistors in series, combine them in parallel, and reverse-engineer a target value from two standard parts, all in the browser

T = 2π√(L/g) — solve a simple pendulum's period, frequency or length, with Earth, Moon and Mars gravity, browser-only

Mass percent of every element in a compound — type a formula, read the breakdown — IUPAC atomic weights, browser-only

Compare a measured value against the true value — get percent error, absolute error, relative error, and signed high/low. Plus a percent-difference mode for two trials with no accepted answer.

actual ÷ theoretical × 100 — solve for percent, actual or theoretical yield, grams or moles, with a plain-English read on why it is below or above 100% — browser-only

Growth rate, drop, percentage-point gap, and reverse-solve the new value — signed, color-coded, browser-only

Any percentile P plus Q1 Q2 Q3, IQR, five-number summary, box plot and 1.5×IQR outliers, browser-only

pH, pOH, [H+] and [OH-] from any one value, with an acid/base verdict and a 0-14 colour scale, all in your browser

Wavelength or frequency in, photon energy out in joules and eV — Planck equation E = hf = hc/λ, with EM band — browser-only

Power ÷ weight in W/kg, hp/ton and kW/kg — cars and cycling, forward and reverse, browser-only

Pixel density, dot pitch, physical size, aspect ratio & a retina check from resolution + diagonal — all in your browser

Test primality · factorize · list primes in a range · find the N-th prime — exact BigInt math, browser-only

Solve flight time, max height, range & impact speed from launch speed, angle and height — with a live trajectory plot, browser-only

Cross two genotypes — Aa × Aa or AaBb × AaBb — get the grid, the genotype ratio and the phenotype ratio, one-click copy, browser-only

Frequency + duty cycle to period, on-time, off-time and average voltage — reverse-solve duty from a measured pulse width — browser-only

Solve a²+b²=c² — find the hypotenuse, find a missing leg, or measure the distance between two points (2D & 3D). Browser-only.

Solve a:b = c:x, simplify ratios, split a total by a ratio, scale a recipe up or down — with full steps, browser-only

τ = R · C — charge and discharge curve, 1τ (63%) and 5τ (99%) markers, Ω/µF auto units — browser-only

Sides n + side length s, get area, interior angle, apothem and both radii, with a to-scale n-gon drawn live, browser-only

Decode 4, 5 and 6-band resistors to Ω, tolerance and tempco — or go the other way, with a live color-band drawing

Tsiolkovsky Δv = ve·ln(m0/mf) — solve from exhaust velocity or specific impulse, reverse-solve propellant, mass ratio, browser-only

Arabic ⇄ Roman, both directions, live — strict validation, step-by-step breakdown, vinculum up to 3,999,999 — 100% browser-only

How many people to survey for a given confidence and margin of error — finite-population correction, reverse mode, one-click copy, browser-only

R_s = 2GM/c² — turn any mass into its black-hole event horizon, in metres, km or light-seconds, with presets and inverse solve — browser-only

Plain ⇄ scientific (a×10ⁿ) ⇄ engineering ⇄ E-notation — with significant figures, exact big/small numbers — browser-only

Count sig figs · round to N significant figures · do sig-fig arithmetic — exact string-level math, browser-only

Reduce any fraction to lowest terms, see the GCD it divided by, and flip between improper and mixed forms, all in your browser

Two points in, full line out — slope, angle, distance, midpoint, y = mx + b and grade % — browser-only

n1·sin(θ1) = n2·sin(θ2) — solve refraction angle, critical angle and total internal reflection — browser-only

Type one integer, see at a glance whether it is prime, perfect, abundant, deficient, triangular, square, cube, Fibonacci, palindrome, with the reason for each, browser-only

Q = m·c·ΔT — solve for any of heat, mass, specific heat or temperature change, with water/aluminum/iron/copper presets and J/kJ/cal units — browser-only

Type any one of radius, diameter, volume or surface area — the other three solve instantly, plus how many liters the ball holds — browser-only

P = εσAT⁴ — radiated power, radiant exitance and the inverse (power → temperature), with Sun and body presets — browser-only

Step angle + microstepping + transmission → steps/rev, steps/mm, steps for any travel — Marlin/Klipper config, browser-only

Turn any BPM into a full delay-time table — milliseconds and Hz for every note value, plus dotted and triplet. Built for mixing and producing.

Answers wrong → percent + letter grade + a full printable grading chart — the teacher's EZ Grader, browser-only

P = √3 · VL · IL · cosφ — active kW, apparent kVA, reactive kVAR and reverse line current — browser-only

Np/Ns = Vp/Vs = Is/Ip — turns ratio, secondary voltage, current and impedance transform, step-up vs step-down — browser-only

Triangle solver — SSS, SAS, ASA, AAS, and the ambiguous SSA case via law of sines + law of cosines. All sides, angles, area, perimeter, type, drawn to scale.

Add, subtract, scale, dot, cross, magnitude, angle, unit vector and projection for 2D and 3D vectors — browser-only

File size = bitrate × duration ÷ 8 — solve any one of bitrate, length or size, add audio, copy in one click — browser-only

Vout = Vin · R2 / (R1 + R2), reverse-solve any resistor, see current, power and how a load drags the output down. Browser-only.

Wire and cable voltage drop from current, run length, conductor size and material, with the 3% limit check, copper vs aluminium, single-phase and three-phase, browser-only

Convert between wavelength λ, frequency f, and photon energy E · c = λf · E = hf · spectrum band + visible colour · browser-only

Any value × weight pairs, weighted mean = Σ(value×weight)/Σweight, plus plain average and per-row contribution, browser-only

Items + weights → your current course grade, with letter and banked points — browser-only

AWG to mm, area, ampacity and resistance, both ways, with a full 4/0 to 40 reference chart, browser-only

W = F·d·cosθ and P = W/t — solve work, power or force, with angle, P = F·v and HP ⇄ W — browser-only

Convert a three-terminal resistor network between wye (Y / T) and delta (Δ / π) — Δ→Y and Y→Δ both directions, exact formulas, one-click copy — browser-only

Standardize any value, reverse a z-score back to raw, or compute μ and σ from a dataset — with left/right/two-tailed normal probabilities and percentile

BaZi (Four Pillars) calculator — Chinese metaphysics birth chart with 8 characters, five elements analysis.

Chinese zodiac checker — your animal sign, element, compatibility, lucky numbers/colors by birth year.

Chinese zodiac fortune — daily/monthly/yearly outlook for 12 zodiac signs in love, career, wealth, health.

Chinese zodiac compatibility — match two people by their zodiac signs, 144 pair combinations with reading.

Western zodiac calculator — your sign, element, ruling planet, compatibility, daily traits.

Gregorian ⇄ Chinese Lunar (Nongli) calendar — bi-directional, accurate 1900-2100.

Arabic ⇄ Chinese number — simple (一二三), formal (壹貳參), or amount (金额大写 with 元角分).

Chinese character stroke counter — count strokes for any hanzi, traditional or simplified.

Chinese lunar almanac (huangli) — daily 宜/忌 advice, 24 solar terms, 干支/生肖, auspicious hours, any date 1900-2100.

China marriage betrothal reference — 30+ provinces' typical betrothal money + dowry + 3-gold/5-gold averages (2024-2026 public data).

China retirement age calculator (2025 reform) — exact retirement date by birth year + gender + worker category, per Sept 2024 NPC reform.

Color mixer — blend any two colors with adjustable ratio, RGB/HSL/LAB color space, predict the result and copy hex.

24-point solver and game — enter 4 numbers and get every solution instantly, or play random hands against the clock.

AI token counter — estimate token count for GPT / Claude / Gemini, with per-model cost calculator (2026 pricing).

Add, subtract, multiply and divide two binary numbers, exact BigInt math, results in binary, decimal, hex and octal, browser-only

Left shift, logical and arithmetic right shift — see the bits move, pick 8/16/32-bit, read decimal, hex and binary — browser-only

Track billable hours by task — auto subtotals, grand total, blended rate, CSV export.

Plain number ⇄ engineering notation (×10³ⁿ) ⇄ SI prefix (47kΩ) — exponent always a multiple of 3, with scientific notation for contrast — browser-only

2048 game — slide tiles, combine numbers, reach 2048. Pure browser, no ads, your high score saved locally.

Find duplicates and keep one clean copy of iso dates from pasted text or uploaded local files.

Extract, dedupe, and export iso dates from pasted text or uploaded local files.

Convert iso dates from pasted text or uploaded local files.

Validate and explain issues in iso dates from pasted text or uploaded local files.

Normalize, sort, and prepare iso dates from pasted text or uploaded local files.

Gregorian date ⇄ Julian Day Number (JDN), fractional JD, Modified Julian Date (MJD) and ordinal day-of-year — astronomy-grade, browser-only

Percent ⇄ fraction, both ways. 25% becomes 1/4, 3/4 becomes 75%, decimal percents and values over 100% included, fully reduced, browser-only.

Convert (x, y) to (r, θ) and back, degrees or radians, with a live coordinate diagram, browser-only

Sudoku generator and solver — 4 difficulties (easy / medium / hard / expert), unique-solution guaranteed, play in the browser or print as PDF.

Solve any of words, minutes, and WPM — paste a speech to estimate read-aloud time, with speaking-rate presets and one-click copy — browser-only

Chinese characters to pinyin — with tone marks or numbers, supports simplified and traditional.

800+ everyday chengyu — pinyin, origin, usage.

Chinese classical poetry — 300+ hand-annotated Tang/Song/Yuan canon (唐诗宋词元曲) plus 80,000+ searchable Tang/Song/Shijing/Chuci poems on demand.

Chinese name generator — meaningful Chinese names with pinyin, meaning, and stroke count.

Chinese character stroke counter — count strokes for any hanzi, traditional or simplified.

Chengyu chain game with a 30,000+ idiom dictionary (full 汉语成语大词典 coverage). Start with any idiom; the computer continues with one whose first character matches your last.

Traditional ⇄ Simplified Chinese — fast, character-level, no API.

Five Elements (Wuxing) name recommender — based on Bazi gaps, suggest characters that balance the missing elements.

Handwriting practice sheet generator — Chinese 米字格 / 田字格 / 四线三格 (English) PDF-ready printable.

Hanyu Pinyin to Zhuyin ㄅㄆㄇㄈ both ways, tone marks ˊˇˋ˙, batch by space, copy in one click, runs in your browser

English vocabulary test — estimate your vocab size in 5 minutes, levels CET-4 / CET-6 / IELTS / TOEFL / GRE.

English grammar rules reference — 60+ core grammar rules with side-by-side examples, common mistakes, bilingual explanations.

English collocations reference — 200+ common verb + noun / adj + noun / verb + prep collocations with usage examples.

English irregular verbs reference — 200+ verbs with base / past / past participle, Chinese gloss, in-browser audio, pattern filter, and a flash-card practice mode.

HSK Chinese vocabulary test — estimate your Mandarin level (HSK 1-6) in 5 minutes with real exam words.

Turn singular English nouns into plurals and back, with irregulars, -ies, -ves and uncountables handled, all in your browser

Paste English text and get Flesch Reading Ease plus five grade-level scores, syllable counts, and reading time — runs entirely in your browser

Count syllables in any English word or text, with a 5-7-5 haiku mode for poems

Capitalize an English title the way editors do, AP / Chicago / APA / MLA, small words stay down, acronyms kept, runs in your browser

Arabic 1100 essential A1–A2 MSA words — Arabic script with full ḥarakāt, DIN 31635 romanization, gender, three-form verbs, audio TTS.

Dutch 500 essential A1–A2 words — IPA + de/het articles + 6-person conjugation + audio TTS.

1086 French entries — 1036 DELF A1-B2 core words plus 50 profession words. IPA, gender, Bescherelle conjugation (présent / passé composé / futur simple), free TTS, 17 categories.

German 500 essential words (A1-A2 + B1 core) with IPA, der/die/das, full Präsens, Präteritum, Perfekt, Partizip II for verbs, and browser TTS.

Hindi 1300 essential A1–A2 words — Devanagari, IAST, IPA, gender, -nā verbs, audio TTS.

Indonesian 500 essential A1–A2 words — KBBI spelling + Jakarta IPA + audio TTS. No tones, no conjugation.

Italian 500 essential words (A1-A2 Plida) with IPA, gender, full verb conjugation, audio TTS.

Japanese 500 essential words covering JLPT N5 and N4, with kana, romaji, kanji and audio TTS.

Korean 500 essential words spanning TOPIK I and TOPIK II — start speaking Korean today with Hangul, romanization, audio TTS, and full verb conjugations.

Portuguese 500 essential words — A1 to A2 Brazilian Portuguese, with IPA, gender, conjugation, audio TTS.

Russian 500 essential words covering the full TORFL A1-A2 syllabus, with Cyrillic, stress marks, BGN/PCGN romanization, gender, full verb conjugation, and audio TTS.

Spanish 500 essential A1–A2 words — start speaking Spanish today, with pronunciation, example sentences, verb conjugations and audio TTS.

Thai 500 essential A1–A2 words — Thai script + RTGS + IPA + 5 tones + audio TTS.

Turkish 500 essential A1–A2 words — Istanbul standard + IPA + vowel harmony + audio TTS.

Vietnamese 500 essential A1–A2 words — chữ Quốc ngữ + IPA + 6 tones + audio TTS.

Headline analyzer — score your title's clickability, SEO length, emotional words, power words.

Slogan generator — 30+ proven copywriting formulas, generate brand slogans in seconds, bilingual.

Hashtag generator — Instagram / TikTok / Twitter / Xiaohongshu / Weibo hashtags from your topic.

Cover letter generator — fill 6 fields, pick a tone, get a tailored cover letter in 4 templates, bilingual.

Resume template builder — fill a form, get a clean PDF resume in 3 templates (modern / classic / minimal), bilingual.

Interview questions bank — 300+ real questions across behavioral / technical / case / culture, with strong answer frameworks.

200+ prompt templates for ChatGPT, Claude, Gemini — copy-paste, browse by use case.

Turn role, task, constraints, and output rules into a structured system prompt you can copy.

Generate eval cases, pass criteria, and edge cases from an AI feature, risks, and user path.

AI model comparison — 20+ models (GPT / Claude / Gemini / Llama / Qwen) across price, context, speed, capabilities (2026).

AI token counter — estimate token count for GPT / Claude / Gemini, with per-model cost calculator (2026 pricing).

Generate a prioritized content refresh checklist from URL, topic, and performance signals.

Generate SEO meta description options from a page topic, keywords, and audience.

Score a YouTube title for clarity, specificity, length, and keyword position.

Weekly report generator — fill blanks, get clean markdown, no AI hallucination.

Random names from 11 cultures — Chinese, English, Japanese, Korean, Arabic, Russian + 5 European.