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Unit converter

Convert length, mass, temperature, time, speed, area and volume between metric and imperial units as you type. For maths and science homework, recipes and travel; it works offline once loaded.

Learn this properly

Lessons from the Maths course on this topic: worked steps, then exam-style questions with new numbers every time.

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How it works

This unit converter handles the conversions that come up in science, maths and everyday homework: length, mass, temperature, time, volume, area, speed and digital data. Type a number on either side and the other side updates as you type, with the conversion factor shown underneath so you can check your own working.

  1. Pick a category tab: Length, Mass, Temperature, Time, Volume, Area, Speed or Data.
  2. Choose the unit you are converting from and the unit you want in the two drop-down menus.
  3. Type your value in the From box. The result appears in the To box straight away.
  4. To convert the other way, type in the To box instead, or press the swap button between the boxes to flip the two units.
  5. Read the line under the boxes: it shows what one of your starting unit is worth in the target unit, or the full working for temperature.

Tips

  • Use the factor line to check textbook answers. If it says 1 Inch = 2.54 Centimetre, multiplying your inches by 2.54 should match your own calculation.
  • Temperature does not convert with a single factor because the scales start at different zeros. Learn the rules: Fahrenheit = Celsius x 9/5 + 32, and Kelvin = Celsius + 273.15.
  • In physics, convert everything to SI units (metres, kilograms, seconds) before using a formula. Speed in km/h is a common trap: change it to m/s first.
  • The Data category uses 1 kilobyte = 1024 bytes. Some courses use 1000 instead, so check which one your teacher expects.

FAQ

Which units are included?
Length runs from millimetres to miles, including inches, feet and yards. Mass covers grams, kilograms, tonnes, ounces, pounds and stone. Volume has US cups, pints and gallons alongside millilitres, litres and cubic metres. Area includes hectares and acres, Speed has m/s, km/h, mph and knots, and Time goes from seconds to weeks.
How accurate are the results?
Results are rounded to six decimal places, and very large or very small conversion factors are shown in scientific notation. Imperial units use standard rounded factors, which is more than precise enough for schoolwork.
Does it save anything?
It remembers your last category and the units you picked in each one, in this browser's local storage on this device. Nothing is uploaded unless you sign in to an optional free Brainlag account, which syncs it across devices. Clearing your browser data resets it.

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