Unit Converter
Convert between metric and imperial across length, mass, volume, area, speed and temperature.
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How it works
Every unit here is defined against a base unit for its dimension — metres, kilograms, litres, square metres or km/h — so a conversion is a single multiplication through that base. The definitions are the exact international ones, not rounded approximations.
Temperature is the exception. Celsius, Fahrenheit and Kelvin have different zero points as well as different scales, so they convert through explicit formulas rather than a factor.
Result = value × (from unit’s factor ÷ to unit’s factor)
- Dimension — the physical quantity — length, mass, volume, area, speed or temperature
- Base unit — the reference every unit in a dimension converts through
- Exact definitions — 1 inch = 25.4 mm and 1 pound = 0.45359237 kg, by international agreement
Worked example
Converting 26.2 miles to kilometres
Inputs
Results
The marathon distance. The conversion factor is exact by definition, not an approximation.
Frequently asked questions
Why does it say the units do not match?
Because you have picked units from two different dimensions — kilograms and metres, for instance. There is no meaningful conversion between them, so the calculator refuses rather than returning a misleading number.
Which gallon does it use?
Both are available and they differ substantially: a US gallon is 3.785 litres, a UK gallon is 4.546. Picking the wrong one introduces a 20% error, so the two are listed separately.
How precise are the conversions?
They use the exact internationally agreed definitions. Results are shown to a sensible number of decimal places, but the underlying arithmetic carries full precision.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Nothing you type is transmitted to us or stored.
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