Unit Converter
Convert length, weight, temperature, volume, area, speed and data — instantly.
Common conversions & formulas
The converter updates as you type, but here are the factors behind the most common metric-to-imperial conversions.
| Conversion | Formula | Example |
|---|---|---|
| Centimeters to inches | cm ÷ 2.54 | 10 cm = 3.94 in |
| Meters to feet | m × 3.28084 | 5 m = 16.40 ft |
| Kilometers to miles | km ÷ 1.60934 | 5 km = 3.11 mi |
| Kilograms to pounds | kg × 2.20462 | 10 kg = 22.05 lb |
| Celsius to Fahrenheit | (°C × 9/5) + 32 | 20 °C = 68 °F |
| Liters to gallons (US) | L ÷ 3.78541 | 10 L = 2.64 gal |
How conversion works
Most units are linear: each value is turned into a base unit (meters, grams, liters…) and then into your target unit, which keeps every result consistent. Temperature is different because the scales don’t share a zero point, so it uses formulas instead of a single factor.
How conversion actually works
Every unit conversion is a multiplication by a ratio that equals one. A metre and 3.28084 feet are the same length, so the fraction (3.28084 ft / 1 m) has a value of one and multiplying by it changes the label without changing the quantity. Chain those ratios and you can get from any unit to any other in the same family.
Temperature is the exception: Celsius and Fahrenheit have different zero points, so they need an offset as well as a scale factor.
Exact factors worth memorising
Several of the imperial-to-metric factors are exact by international agreement rather than measured, which is why they never change.
| Conversion | Factor | Status |
|---|---|---|
| 1 inch | 25.4 mm | Exact by definition |
| 1 foot | 0.3048 m | Exact |
| 1 mile | 1,609.344 m | Exact |
| 1 pound | 0.45359237 kg | Exact |
| 1 troy ounce | 31.1034768 g | Exact |
| 1 US gallon | 3.785411784 L | Exact |
| 1 imperial gallon | 4.54609 L | Exact |
| 1 nautical mile | 1,852 m | Exact |
Traps that cause real errors
- US vs imperial volume. A US gallon is about 17% smaller than an imperial gallon, and a US pint is 16 fl oz against the imperial 20. Recipes and fuel-economy figures cross this line constantly.
- Ounces are two different things. A troy ounce (precious metals, 31.103 g) is heavier than the everyday avoirdupois ounce (28.35 g). See grams in an ounce.
- Weight versus mass. Kilograms measure mass, pounds-force measure weight. On Earth the conversion is harmless; in physics problems it is not.
- Data units. A kilobyte can mean 1,000 bytes (drive manufacturers) or 1,024 bytes (operating systems). The unambiguous binary units are KiB, MiB and GiB.
- Fuel economy inverts. Miles per gallon and litres per 100 km run in opposite directions, so you divide rather than multiply: 235.215 ÷ mpg = L/100 km.
Rounding sensibly
Carry full precision through the calculation and round only at the end, to the precision of your least accurate input. Converting a measurement given as “about 5 feet” into 1.524 metres implies millimetre accuracy you never had — 1.5 m is the honest answer.
Unit converter FAQ
How do you convert between metric and imperial units?
How many centimetres are in an inch?
How do I convert Celsius to Fahrenheit?
Is a US gallon the same as an imperial gallon?
What is the difference between a troy ounce and a regular ounce?
Why do file sizes differ between my drive and my computer?
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