Unit converter
Convert between metric, US and imperial units in either direction, and see the value in every unit at once.
Runs entirely in your browser
In every unit
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Results are rounded to the number of significant figures you choose (10 by default, up to 12). Factors are the exact legal definitions, so the only rounding is in the last digit shown.
How to convert units
- Pick what you are measuring: length, weight, temperature, volume, area or speed.
- Type a value and choose the units to convert from and to. You can type in either box; the other one updates.
- Read the conversion and the formula, or look down the table for the same value in every unit.
How the conversions work
Each category has a base unit: metres for length, kilograms for weight, litres for volume, square metres for area and metres per second for speed. A value is multiplied by its unit's size in the base unit, then divided by the size of the target unit. Because every factor is an exact definition (1 inch = 0.0254 m exactly, 1 pound = 0.45359237 kg exactly), the result is as precise as the numbers you type.
Temperature works differently because the scales have different zero points. Celsius and Kelvin share a degree size but Kelvin starts at absolute zero, so K = °C + 273.15. Fahrenheit degrees are 5/9 the size of Celsius degrees and the scale is shifted, so °F = °C × 9/5 + 32. Rankine is the Fahrenheit-sized scale that starts at absolute zero.
Some units share a name but not a size. US and UK gallons, pints and fluid ounces differ, and so do US, UK and metric tons, so they are listed separately and labelled.
Tips
- Working out a share or a markup after converting? Use the percentage calculator.
- Scaling a picture or a screen size? The aspect ratio calculator keeps proportions.
- Converting time spans rather than units? The date difference calculator counts days, weeks and months between dates.
Questions
How accurate are the conversions?
The factors are exact by definition: an inch is 2.54 cm, a pound is 0.45359237 kg, a US gallon is 3.785411784 litres, a nautical mile is 1,852 metres. The only rounding is in the result, which is shown to 10 significant figures unless you choose otherwise.
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785411784 litres and a UK (imperial) gallon is 4.54609 litres, about 20% more. US and UK pints and fluid ounces differ too, so the units are labelled US or UK. A UK pint is 20 UK fluid ounces; a US pint is 16 US fluid ounces.
Which cup does it use?
The US customary cup, a sixteenth of a US gallon: 236.5882365 mL. US nutrition labels round a cup to 240 mL, and recipes from Australia, Canada and New Zealand often use a 250 mL metric cup, so check which one your recipe means.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: 20 °C is 20 × 9/5 + 32 = 68 °F. To go back, subtract 32 and multiply by 5/9. The scales meet at −40, where −40 °C equals −40 °F. Temperature is the only category here that isn't a simple multiplication, because the scales start from different zeros.
Why does it warn about absolute zero?
Absolute zero (0 K, −273.15 °C, −459.67 °F) is the lowest temperature possible. A value below it can't be a real temperature, which usually means a typo or a mixed-up unit. The numbers are still converted so you can see what was entered.
What is the difference between a US ton and a tonne?
A tonne (metric ton) is 1,000 kg. A US (short) ton is 2,000 lb, about 907.18 kg, and a UK (long) ton is 2,240 lb, about 1,016.05 kg.