Every common unit in one place
Recipes from abroad, a running route in miles, a room in square metres, a car's speed in kilometres per hour: daily life is full of the wrong units. This unit converter covers the seven kinds people need most, with metric, US and UK units side by side.
Choose the kind of measurement, type an amount and pick the units. The answer appears straight away, with the same amount in every other unit of that kind listed underneath, so one entry answers several questions at once.
How to use it
- Pick the kind of unit: length, area, volume, weight, temperature, speed or time.
- Type the amount. Decimals and negative temperatures are fine.
- Choose the unit you have in From and the one you want in To.
- Read the answer, then the full list of other units below it.
How the conversions work
result = amount × size of the From unit ÷ size of the To unit
°F = °C × 9/5 + 32; K = °C + 273.15Each kind of unit has a base, such as metres for length or litres for volume, and every unit is stored as an exact multiple of it. The US and imperial units are defined exactly in metric terms, as set out in NIST Handbook 44: an inch is 2.54 cm, a pound 0.45359237 kg, a US gallon 231 cubic inches and a UK gallon 4.54609 litres. Temperature is the exception, because its scales start from different zero points, so it uses its own formulas.
Worked example: 5 miles in kilometres
- 1 mile = 1,609.344 metres; 1 kilometre = 1,000 metres
- 5 × 1,609.344 ÷ 1,000 = 8.04672 kilometres
Why so many decimal places? Because the mile is defined exactly in metres, the answer is exact too. Round it to suit the job: 8 km is fine for a training plan, 8.05 km for a race sign.
A 5 mile run is 8.04672 kilometres. The list below the answer shows the same distance as 8,800 yards, 26,400 feet and 316,800 inches.
Handy conversions
| From | To | Value |
|---|---|---|
| 1 inch | centimetres | 2.54 (exact) |
| 1 mile | kilometres | 1.609344 (exact) |
| 1 acre | square metres | 4,046.86 |
| 1 US gallon | litres | 3.785411784 (exact) |
| 1 UK gallon | litres | 4.54609 (exact) |
| 1 pound | kilograms | 0.45359237 (exact) |
| 0 °C | °F | 32 |
| 60 mph | km/h | 96.56 |
Mistakes to avoid
- Mixing US and UK volumes. A UK gallon is about 20% bigger than a US gallon, and pints differ the same way.
- Using a length factor for area. Square units scale by the factor squared: 1 square foot is 0.0929 square metres.
- Converting temperature differences like temperatures. A rise of 10 °C is a rise of 18 °F, not 50 °F.
- Treating a month or a year as an exact number of days. The time conversions use an average year of 365.2425 days. For calendar dates, use the date calculator.
Frequently asked questions
How do I convert between metric and US units?
Multiply by the size of the unit you have and divide by the size of the unit you want, both in the same base unit. For 5 miles to kilometres: 5 × 1,609.344 ÷ 1,000 = 8.05 km. The converter does this for length, area, volume, weight, speed and time, and uses formulas for temperature.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. So 20 °C is 20 × 1.8 + 32 = 68 °F, and 100 °C is 212 °F. To go back, take away 32 and multiply by 5/9. Choose Temperature above for any value, including Kelvin.
What is the difference between US and UK gallons?
A US gallon is 231 cubic inches, about 3.785 litres. A UK, or imperial, gallon is exactly 4.54609 litres, about 20% larger. Pints follow the same pattern. The converter lists both, so pick the one used where your recipe, fuel price or tank size comes from.
How accurate is this unit converter?
The factors are exact definitions, so the only rounding is in how the answer is shown: up to six significant figures, which is far more than everyday measuring tools can read. Very large or very small answers are shown in scientific notation, like 1.2 × 10^9.
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