Calculator for Developer
68 calculator tools hand-picked for Developer.
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555 Timer Calculator
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
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Age Difference Calculator
The exact gap between two birthdays — years/months/days, percentage, and the date one person is twice the other's age — browser-only
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AI Token Counter
AI token counter — estimate token count for GPT / Claude / Gemini, with per-model cost calculator (2026 pricing).
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Antenna Length Calculator
Frequency in MHz to dipole, quarter-wave and full-wave length, with velocity factor, in metres or feet, browser-only
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Armstrong Number Checker
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.
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Aspect Ratio Calculator
Calculate aspect ratio — fix any 1 of [width, height, ratio], get the other two.
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Number Base Converter
Number base converter — binary, octal, decimal, hex, and any base 2-36. Bitwise too.
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Battery Life Calculator
Capacity ÷ load × efficiency = runtime — mAh and Wh modes, reverse-solve capacity, charge time, share link — browser-only
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Binary Calculator
Add, subtract, multiply and divide two binary numbers, exact BigInt math, results in binary, decimal, hex and octal, browser-only
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Bit Shift Calculator
Left shift, logical and arithmetic right shift — see the bits move, pick 8/16/32-bit, read decimal, hex and binary — browser-only
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Business Days Calculator
Working days between two dates, or a date N working days out — weekends + holidays excluded, browser-only
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Capacitor Code Calculator
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
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Capacitor Energy Calculator
E = ½CV² stored energy + charge Q = CV — solve any one of C, V, E from the other two — browser-only
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Continued Fraction Calculator
Expand a decimal or fraction into a continued fraction [a0;a1,a2,...] with the convergents that best approximate it — browser-only
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Coordinate Distance Calculator
Great-circle distance between two lat/long points with the Haversine formula, plus bearing and midpoint, all in your browser
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Decibel Calculator
Add sound levels, convert ratio ⇄ dB (power 10·log, amplitude 20·log), and read a common-sound reference table — browser-only
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Download Time Calculator
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
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Duration Converter
Seconds ⇄ minutes ⇄ hours ⇄ days ⇄ weeks, plus human-readable, ISO 8601 duration and HH:MM:SS — one input, every format — browser-only
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Engineering Notation Converter
Plain number ⇄ engineering notation (×10³ⁿ) ⇄ SI prefix (47kΩ) — exponent always a multiple of 3, with scientific notation for contrast — browser-only
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Frequency Wavelength Calculator
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
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GC Content Calculator
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.
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Happy Number Checker
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.
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Horsepower Torque Calculator
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
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ISO Date Deduplicator
Find duplicates and keep one clean copy of iso dates from pasted text or uploaded local files.
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ISO Date Extractor
Extract, dedupe, and export iso dates from pasted text or uploaded local files.
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ISO Date List Converter
Convert iso dates from pasted text or uploaded local files.
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ISO Date List Validator
Validate and explain issues in iso dates from pasted text or uploaded local files.
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ISO Date Normalizer
Normalize, sort, and prepare iso dates from pasted text or uploaded local files.
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Julian Date Converter
Gregorian date ⇄ Julian Day Number (JDN), fractional JD, Modified Julian Date (MJD) and ordinal day-of-year — astronomy-grade, browser-only
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LC Resonance Frequency Calculator
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
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LED Resistor Calculator
R =(Vs − n·Vf)/ If, with nearest E12/E24 value, resistor wattage and a dark-LED check, browser-only
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LED Strip Power Calculator
W/m × length = total watts · watts ÷ volts = amps · +20% headroom sizes the supply · 5V / 12V / 24V · browser-only
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Linux Permission (chmod) Calculator
Linux permission (chmod) calculator — convert between octal (755), symbolic (rwxr-xr-x), and ls -l forms, with safety warnings.
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LLM Pricing Calculator
Estimate daily and monthly LLM spend from tokens, request volume, and editable model prices.
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Logarithm Calculator
log_b(x), ln, log₁₀, log₂ and antilog in one place — change-of-base steps shown, one-click copy, browser-only
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Low Pass Filter Cutoff Calculator
RC and LC filter −3 dB cutoff frequency · fc = 1/(2πRC) · reverse-solve the capacitor or resistor · browser-only
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Meeting Cost Calculator
Meeting cost calculator — see how much that meeting is costing in real-time, with team salary data and overhead multiplier.
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Modulo Calculator
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
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Number Formatter
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.
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Ohm's Law Calculator
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.
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Op-Amp Gain Calculator
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
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Parallel & Series Resistor Calculator
Add resistors in series, combine them in parallel, and reverse-engineer a target value from two standard parts, all in the browser
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Polar / Rectangular Coordinate Converter
Convert (x, y) to (r, θ) and back, degrees or radians, with a live coordinate diagram, browser-only
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Pomodoro Timer
Pomodoro timer — 25/5 classic, plus 50/10 and 90/15 long-focus modes, with sound, browser tab title, daily stats.
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Power-to-Weight Ratio Calculator
Power ÷ weight in W/kg, hp/ton and kW/kg — cars and cycling, forward and reverse, browser-only
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PPI Calculator
Pixel density, dot pitch, physical size, aspect ratio & a retina check from resolution + diagonal — all in your browser
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Prime Number Calculator
Test primality · factorize · list primes in a range · find the N-th prime — exact BigInt math, browser-only
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PWM Duty Cycle Calculator
Frequency + duty cycle to period, on-time, off-time and average voltage — reverse-solve duty from a measured pulse width — browser-only
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PX REM EM Converter
CSS px ↔ rem ↔ em converter — visual scale, base font size adjustable.
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RC Time Constant Calculator
τ = R · C — charge and discharge curve, 1τ (63%) and 5τ (99%) markers, Ω/µF auto units — browser-only
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Resistor Color Code Calculator
Decode 4, 5 and 6-band resistors to Ω, tolerance and tempco — or go the other way, with a live color-band drawing
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Rocket Equation Delta-v Calculator
Tsiolkovsky Δv = ve·ln(m0/mf) — solve from exhaust velocity or specific impulse, reverse-solve propellant, mass ratio, browser-only
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Scientific Calculator
Scientific calculator — sin / cos / log / sqrt / power, with full keyboard input + history, deg/rad mode.
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Scientific Notation Converter
Plain ⇄ scientific (a×10ⁿ) ⇄ engineering ⇄ E-notation — with significant figures, exact big/small numbers — browser-only
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Stepper Motor Steps Calculator
Step angle + microstepping + transmission → steps/rev, steps/mm, steps for any travel — Marlin/Klipper config, browser-only
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Story Points to Time Converter
Team velocity + sprint length + team size → what 13 story points actually means in hours, days and sprints — both directions, browser-only.
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Three-Phase Power Calculator
P = √3 · VL · IL · cosφ — active kW, apparent kVA, reactive kVAR and reverse line current — browser-only
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Unix Timestamp Converter
Unix timestamp ⇄ human date — seconds / milliseconds / ISO 8601 — UTC and local — browser-only
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Timezone Meeting Planner
Plan meetings across timezones — see when everyone's working hours overlap.
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Transformer Turns Ratio Calculator
Np/Ns = Vp/Vs = Is/Ip — turns ratio, secondary voltage, current and impedance transform, step-up vs step-down — browser-only
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Typing Speed Test
Typing speed test — WPM, accuracy, real-time mistakes, English + Chinese pinyin modes.
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Vector Calculator
Add, subtract, scale, dot, cross, magnitude, angle, unit vector and projection for 2D and 3D vectors — browser-only
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Video Bitrate Calculator
File size = bitrate × duration ÷ 8 — solve any one of bitrate, length or size, add audio, copy in one click — browser-only
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Voltage Divider Calculator
Vout = Vin · R2 / (R1 + R2), reverse-solve any resistor, see current, power and how a load drags the output down. Browser-only.
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Voltage Drop Calculator
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
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Week Number Calculator
What week number is today? ISO 8601 (Mon-start) + US (Sun-start), plus year + week → date range — browser-only
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Wire Gauge Calculator (AWG)
AWG to mm, area, ampacity and resistance, both ways, with a full 4/0 to 40 reference chart, browser-only
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Wye-Delta Resistor Calculator
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