Converters
Unit converter
Ten categories of units, from length to pressure: pick the one you need, type the value and read the conversion as you write.
How conversions work
Almost every conversion is a multiplication by a fixed factor. Each category has a reference unit — the metre for lengths, the kilogram for masses, the joule for energy — and every other unit is defined by how many reference units it is worth. Converting from one unit to another therefore means multiplying by the first factor and dividing by the second, in a single step that picks up no intermediate rounding.
Temperature is the exception, because its scales do not share an origin. Celsius and Fahrenheit differ both in slope (one degree Celsius is worth 1.8 degrees Fahrenheit) and in zero point: the conversion is °F = °C × 1.8 + 32, not a plain multiplication. Kelvin shares the Celsius slope but starts from absolute zero, 273.15 degrees lower. This is why a temperature difference converts differently from an absolute temperature.
Digital data deserves a note of its own, because two systems coexist. Decimal prefixes (kB, MB, GB) are powers of 1,000, as everywhere else in the SI system, and they are what drive manufacturers quote. Binary prefixes (KiB, MiB, GiB) are powers of 1,024 and are what many operating systems use to measure space. That is where the surprise of the 1 TB drive shown as 931 GB comes from: the same bytes, counted under two different conventions.
Some units have more than one definition, and it pays to know which you are using. The US gallon (3.785 litres) is not the imperial one (4.546 litres). The metric tonne is a thousand kilograms, while the American short ton is 907.18. This page always states the variant in the unit's name, so the result stays checkable.
Common mistakes
- Converting a temperature as if it were a plain factor: 20 °C is not 20 × 1.8 = 36 °F, because the 32-degree offset has to be added as well.
- Mixing up US and imperial gallons, or the metric tonne and the short ton: the difference is over 20% and slips by easily.
- Treating kB and KiB as synonyms: on a small file the difference is negligible, on a one-terabyte drive it exceeds 90 GB.
- Getting the exponent wrong in area and volume conversions: a metre is 100 centimetres, but a square metre is 10,000 of them and a cubic metre a million.
- Rounding at every intermediate step rather than only at the end: across a chain of conversions the error builds up quickly.
Frequently asked questions
How do you convert Celsius to Fahrenheit?
°F = °C × 1.8 + 32. Twenty degrees Celsius is therefore 68 °F. The reverse formula is °C = (°F − 32) / 1.8. The two scales meet at −40 degrees, the only point where both readings are the same.
How many kilometres are there in a mile?
A statute mile is exactly 1.609344 kilometres. A nautical mile is 1.852 kilometres exactly, because it is defined as one minute of arc along a meridian: they are two different units that merely share a name.
Why does a 1 TB drive show less space?
The manufacturer counts 1 TB as a thousand billion bytes, while the operating system often measures in tebibytes, that is powers of 1,024. The same bytes then read as roughly 931 GiB: nothing is missing, only the unit counting them has changed.
What is the difference between a calorie and a kilocalorie?
A kilocalorie is a thousand calories. Nutrition labels almost always give kilocalories, even when they say "calories": the 2,000 calories of a diet are really 2,000 kcal, that is 8,368 kilojoules.
Does the converter work offline?
The conversion factors are physical constants and definitions, not rates that change, so the calculation happens entirely in your browser and needs no call to a server once the page has loaded.
How this calculation works
For every category except temperature: converted value = value × factor of the source unit / factor of the target unit, where each factor expresses what that unit is worth in the category's reference unit. Temperature goes through kelvin with affine transformations: K = °C + 273.15, K = (°F − 32) / 1.8 + 273.15, K = °R / 1.8, and back again through the inverses.
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