Category
Convert
Significant digits (not decimal places); very large or small values switch to scientific notation.
Convert to every other unit
Common conversions
Features
- 14 categories, 212 units: length, area, volume, mass, time, speed, temperature, pressure, power, energy, data storage, fuel economy, angle and number bases.
- Converts as you type - changing the category, the units or the number updates the result immediately. One click swaps the two directions, and the whole category can be listed at once.
- Factors are exact definitions (1 in = 2.54 cm, 1 lb = 453.59237 g, 1 US gal = 3.785411784 L); approximations such as the year, the month and Mach are spelled out in each unit's note.
- Seven temperature scales: Celsius, Fahrenheit, Kelvin, Rankine, Delisle, Reaumur and Romer. They are not simple rescalings, so each has its own forward and inverse function.
- Fuel economy puts L/100km, US mpg, UK mpg and km/L in one category. They are reciprocals, not proportional, and multiplying by a constant would give wrong numbers - this page uses a reciprocal model.
- Data storage lists decimal (kB/MB/GB) and binary (KiB/MiB/GiB) units side by side; base conversion uses BigInt, so integers hundreds of digits long keep every digit.
- No backend and no network requests: the value you type only lives in your own browser's localStorage. UI available in English / Simplified / Traditional Chinese.
How to use
- Pick a category at the top (say Length), type a number, choose the source unit, and the target unit's value appears on the right.
- Press Swap to exchange the two units; click any row in the results list to make that unit the target.
- Tick 'Convert to every other unit' to see the whole category at once, and lower 'Precision' if the output gets too long.
- For fuel, decide whether you want 'litres per 100 km' or 'miles per gallon'; for storage, mind that GB and GiB differ by about 7%.
FAQ
- Why is 1 GB not 1 GiB?
- GB is decimal (1 GB = 10^9 bytes) while GiB is binary (1 GiB = 2^30 = 1,073,741,824 bytes) - a gap of about 7%. Drives are sold by GB and operating systems report GiB, which is why a '500 GB' disk shows up as 465 GiB. Both families sit in the same category here so you can see the difference.
- Why do people get fuel economy conversions wrong?
- Because L/100km and mpg are reciprocals, not proportional: 10 L/100km is 23.52 US mpg, but 20 L/100km is not 47 mpg - it is 11.76. Multiplying 'litres per 100 km' by a constant can never give 'miles per gallon'. This page converts through an intermediate litres-per-kilometre quantity.
- When does the result switch to scientific notation?
- Whenever the absolute value is below 10^-6 or at or above 10^16 (for example 1.23e-7); everything else is written in fixed notation with thousands separators. The digit count follows 'Precision' - raise it if you want more digits.
- Which standard do the Chinese customary units follow?
- The current market system: 1 jin = 500 g, 1 liang = 50 g, 1 li = 500 m, 1 zhang = 10 chi = 100/3 m and 1 mu = 2000/3 m^2. Historical regional variants (the Taiwanese jin of 600 g, for instance) are not included; compare against kilograms in the results list if you need those.
- How precise are the results?
- The factors themselves are exact definitions, but arithmetic happens in IEEE-754 double precision, so past roughly 15-17 significant digits you are looking at rounding noise - that is why precision stops at 12. Base conversion is the exception: it is computed digit by digit with BigInt.
About
Unit Converter keeps the whole workflow - category, number, source unit, result - on one page: 14 categories and 212 units covering metric, imperial, US customary, nautical and astronomical units, Chinese market units, plus the three special cases of temperature scales, fuel economy and number bases. It matches w3ctool.com/tools/unit-converter and adds a full-category table, a common-conversion overview and arbitrary-length base conversion.
Every factor lives in the page's own static data (UnitConvert/unitcore.js?v=7d2f59d3) and the arithmetic runs in your browser: no backend, no network request, so the page keeps working offline once loaded. Your inputs are stored only in this device's localStorage - the site never sees them.
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Runs entirely in your browser · exact definition factors · free · English / 简体 / 繁體