Convert between length, weight, temperature, area, volume, speed, time — instant, browser-only
- Runs locally
- Category Calculator
- Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.
What this tool does
Free online unit converter covering 7 measurement domains: length (mm → mi), weight (mg → ton), temperature (°C ↔ °F ↔ K), area (mm² → km²), volume (mL → gal), speed (km/h ↔ mph ↔ m/s ↔ knot), time (ms → year). High precision (15 significant digits), handles negative input, and shows the conversion factor so you can verify. 100% client-side.
Tool details
- Input
- Numbers
- The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
- Output
- Live result + Copy
- The result area focuses on usable output, with copy, download, or preview actions when supported.
- Privacy
- Browser-side processing
- The main tool logic does not call an external API, so inputs normally stay in the current tab.
- Save / share
- No account required
- Open the page and use it; whether results survive refresh depends on the tool.
- Performance budget
- Initial JS <= 10 KB
- No WASM budget is declared, keeping the tool quick to open on mobile.
- Best fit
- Calculator · Student
- Category and role tags drive related tools, internal links, and quick fit checks.
How to use
-
1. Input
Paste or drop your content into the tool panel.
-
2. Process
Click the button. All processing is local in your browser.
-
3. Copy / Download
Copy the result or download to disk in one click.
How Unit Converter fits into your work
Use it for fast estimates, comparisons, and planning numbers before you make the final call.
Calculation jobs
- Getting a realistic range before a purchase, plan, workout, or schedule decision.
- Comparing scenarios by changing one input at a time.
- Turning rough assumptions into a number you can discuss.
Calculation checks
- Double-check units, dates, rates, and rounding assumptions.
- Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
- Save the inputs that produced an important result so you can reproduce it later.
Good next steps
These links move the current task into a more complete workflow.
- 1 Percentage Calculator 5 common percentage calculations — "x% of y", "x is what% of y", percentage change, increase/decrease — instant, browser-only Open
- 2 Date Difference Calculator Days / weeks / months / years between two dates — plus business-days mode — browser-only Open
- 3 Concrete Calculator Slab, column, round footing & stairs → cubic meters/yards + cement bags, sand and gravel — browser-only Open
Real-world use cases
Scaling a recipe from a US food blog into metric for your kitchen
A cookie recipe lists 2 cups of flour and 350 °F. You bake by grams and Celsius. Convert volume to roughly 473 mL (then weigh it), and 350 °F to 176.67 °C, which you round to 175 for the dial. The factor readout lets you sanity-check that 1 cup really is 236.59 mL before you trust the number.
Filling out an international shipping form that wants kilograms
Your parcel reads 4 lb 6 oz on a US scale, but the carrier portal only accepts kg with two decimals. Convert 4.375 lb to 1.98 kg and the 14 × 10 × 6 in box to 35.56 × 25.4 × 15.24 cm. Getting the rounding right here keeps you under the next pricing tier instead of one decimal over it.
Checking a car's top speed across mph, km/h and knots for a forum post
A spec sheet quotes 155 mph as the limiter. You convert to 249.45 km/h for European readers and 134.68 knots out of curiosity. Because the tool shows speed as a single domain, you switch units without retyping the value, so one number turns into three comparable figures in seconds.
Converting a server timeout from milliseconds to a human duration
A config says the session lives for 1,800,000 ms and you need to write a docs line in plain words. Convert to 1800 s, then 30 min. Later a cache TTL of 604800 s converts cleanly to exactly 7 days, which reads far better in a changelog than a raw second count.
Common pitfalls
Mixing weight and force. A pound on a scale is mass; 1 kg weighs about 2.205 lb here, but a pound-force in physics is different. This tool converts mass, so use it for shipping, not for thrust figures.
Treating temperature like length. You cannot scale °F to °C by a single multiply. -40 °C is -40 °F, not 0. Pick the two temperature units and let the affine formula handle the +32 offset for you.
Squaring the linear factor for area. 1 m = 3.281 ft does NOT mean 1 m² = 3.281 ft². It is 10.764 ft² because area uses the factor squared. Stay inside the area domain and the tool does the squaring.
Privacy
Every conversion runs as plain JavaScript arithmetic inside your browser tab. The numbers you type never reach a server and are not logged. If you share a result link, the current value and unit selection are encoded into the URL so the recipient sees the same conversion, so avoid pasting a sensitive figure into the field if you plan to share that link.
FAQ
Tool combos
Folks in your role tend to reach for these alongside this tool.
- 24-Point Solver & Game 24-point solver and game — enter 4 numbers and get every solution instantly, or play random hands against the clock.
- A1C to Blood Glucose Calculator A1C ⇄ estimated average glucose, both ways, mg/dL or mmol/L, with the ADA range — educational, browser-only
- Chinese Acupoint Locator 200+ meridian acupoints / WHO 2008 standard locations / with contraindications, manipulation, and combinations.
- Add Days to Date Calculator Add or subtract days, weeks, months, and years from any date — plus a business-day mode that skips weekends. Runs entirely in your browser.