Units of measurement
Length, mass, temperature, volume and speed. Definitions follow the SI, and factors are exact wherever an exact factor exists.
Open unitsExactly equal
Units, currencies and file formats, converted in one place. Every result shows the arithmetic behind it, so you can check the number before you use it.
See what we convertPick the two formats. Each conversion has a page of its own.
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What we convert
Three kinds of sameness
Different notations, identical value. Pick the one you need.
Currencies
Reference rates for twelve currencies, always shown with the date they were taken. A rate is a snapshot, so we tell you which one you are using.
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Documents, images, audio and video — every pair with a page of its own. Pick the two formats; it all runs here in your browser.
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Why it matters
Rounded is not the same as wrong
Some conversions are exact by definition. One inch is 25.4 millimetres — not approximately, exactly. Others are measurements, and every digit past the measurement is invention.
We show six decimals by default and say when a factor is exact. If you need fewer digits, round at the end, never in the middle.
Defined, not measured
One inch
25.4 mm exactly, agreed in 1959
One metre
The distance light travels in 1/299,792,458 of a second
One kilogram
Fixed by the Planck constant since 2019
The metre, since 1983
Most looked up
Everyday equivalents
- 1 mile1.609344 km
- 1 inch25.4 mm
- 1 kilogram2.204623 lb
- 1 pound453.59237 g
- 100 °F37.777778 °C
- 1 gallon (US)3.785412 L
- 1 foot0.3048 m
- 1 nautical mile1.852 km
Length & area
Mass & volume
Temperature
Currency