Unit Converter
Convert between metric and imperial units for length, weight, volume, time, digital storage and temperature, with exact conversion factors.
A unit converter translates between units of length, weight, temperature, volume, area, speed, time and digital storage. Defined units convert exactly - an inch is precisely 25.4mm and a pound is precisely 0.45359237kg - so there is no rounding error to worry about.
Runs entirely in your browser · no signup · nothing is uploaded · updated 2026-08-29
How to use it
- 1.Pick a category.
- 2.Choose the units you are converting between.
- 3.Enter an amount - the result updates as you type.
Common conversion factors
Defined units convert exactly - an inch is precisely 25.4mm. Volume is where US and imperial diverge, by about 20%.
| From | To | Multiply by | Exact? |
|---|---|---|---|
| Inch | Millimetre | 25.4 | Exact |
| Foot | Metre | 0.3048 | Exact |
| Mile | Kilometre | 1.609344 | Exact |
| Pound | Kilogram | 0.45359237 | Exact |
| Ounce | Gram | 28.349523125 | Exact |
| US gallon | Litre | 3.785411784 | Exact |
| Imperial gallon | Litre | 4.54609 | Exact |
| US fluid ounce | Millilitre | 29.5735 | Rounded |
| US cup | Millilitre | 236.588 | Rounded |
| Metric cup | Millilitre | 250 | Exact |
| Celsius | Fahrenheit | x 9/5, then + 32 | Formula, not a factor |
| Celsius | Kelvin | + 273.15 | Formula, not a factor |
Frequently asked questions
Are the conversion factors exact?
Yes for defined units. An inch is exactly 25.4mm and a pound is exactly 453.59237g by international agreement, not approximations.
Is a kilobyte 1000 or 1024 bytes?
This tool uses 1024, which is what operating systems and developers mean in practice. Storage manufacturers use 1000, which is why a 1TB drive shows as roughly 931GB.
Why is temperature handled separately?
Temperature scales have different zero points, so they need offset arithmetic rather than simple multiplication. Everything else here is a ratio conversion.
US or imperial gallons?
US. A US gallon is 3.785 litres and an imperial gallon is 4.546 - a 20% difference that catches people out constantly.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. Going back, subtract 32 first then multiply by 5/9. Temperature is the one family where you cannot just multiply by a factor, because the scales have different zero points.
Is a kilobyte 1000 or 1024 bytes?
Both, depending on who is asking. Operating systems and developers use 1024. Storage manufacturers use 1000, which is why a 1TB drive shows as 931GB. The unambiguous names for the binary units are kibibyte and mebibyte.
How many millilitres in a cup?
236.6 in the US, 250 in the metric cup used in Australia and much of Europe, and 284 for an imperial cup. Recipes rarely say which, which is why baking by weight is more reliable.
Are US and imperial measurements the same?
Not for volume. A US gallon is 3.785 litres and an imperial gallon is 4.546 - about 20% larger. Length and weight units do match.
The guide behind this tool
3 min readMetric and imperial: which conversions are exact
Which unit conversions are defined exactly, where US and imperial measures diverge, and the volume and temperature traps that produce wrong answers.
3 min readPercentage calculations: the four formulas
Percentage of, percentage change, reverse percentages and percentage points - the four calculations people mix up, and the arithmetic behind each.
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