How to use Unit Converter
- 1Choose a category such as Length or Temperature
- 2Type the value to convert
- 3Pick the From and To units, or press swap
- 4Read the result and the full table of equivalents
What Unit Converter does
Most of the world measures in metric units, while the United States — and the United Kingdom for miles, pints and stones — still uses imperial or customary ones. Recipes, product specs, weather forecasts and travel directions regularly cross between the two, and a wrong conversion factor is easy to make.
Since 1959 the inch has been defined as exactly 2.54 centimetres and the pound as exactly 0.45359237 kilograms, so conversions between the systems are exact rather than approximate. This converter uses those definitions for every unit, and the table underneath shows the value in every unit of the category at once so you rarely need a second conversion.
When to use it
- Cooking from foreign recipes
- American recipes use cups, tablespoons and ounces. Convert them to millilitres and grams — remembering that a cup of flour and a cup of water weigh differently, so volume only converts to volume.
- Travel and driving
- Road signs in miles, rental cars in km/h and fuel in US or UK gallons: the speed and volume categories cover all of them, including the difference between the two gallons.
- Storage that looks smaller than advertised
- A 1 TB drive shows as about 931 GB in Windows because the operating system counts in binary units. The data size category converts between the two exactly.
Unit Converter settings explained
- Length and area
- Millimetres to kilometres, inches to miles and nautical miles, plus square units, hectares and acres for land and floor space.
- Weight
- Milligrams to tonnes, and ounces, pounds and stones. The tonne here is the metric tonne of 1,000 kg.
- Temperature
- Celsius, Fahrenheit and Kelvin. These have different zero points, so the converter uses the proper formulas rather than a single factor.
- Volume
- Millilitres, litres and cubic metres, US teaspoons to gallons, and the larger UK (imperial) gallon of 4.546 litres.
- Speed
- Metres per second, km/h, mph, knots and feet per second.
- Data size
- Decimal units (KB = 1,000 bytes), used by drive makers and networks, and binary units (KiB = 1,024 bytes), used by most operating systems.
Handy exact conversions
| From | Equals |
|---|---|
| 1 inch | 2.54 cm exactly |
| 1 mile | 1.609344 km exactly |
| 1 pound | 0.45359237 kg exactly |
| 1 US gallon | 3.785411784 litres |
| 0 °C | 32 °F and 273.15 K |
Limits and what to expect
- Volume units are US customary except the separately listed UK gallon; UK pints and fluid ounces are not included.
- Cooking conversions are volume to volume only; converting cups to grams depends on the ingredient's density.
- Results show up to ten significant figures; very large or tiny values switch to scientific notation.
Troubleshooting
- My recipe conversion looks wrong
- Check whether the recipe is American or British. A UK pint is 568 ml but a US pint is 473 ml, and older British recipes use imperial fluid ounces that are slightly smaller than US ones.
- Temperature table shows odd negative numbers
- That is expected: 0 °F is −17.8 °C and 0 °C is 273.15 K. Temperature scales start at different points, so values do not scale proportionally as other units do.
- The result has a long decimal
- Some conversions are not whole numbers, such as 1 foot = 0.3048 metres. Round the result to whatever precision your task needs; the copy button copies the full figure.
Your files and your privacy
Conversions are plain arithmetic done in your browser. Nothing you type is sent anywhere, and the page keeps working offline once it has loaded.
What to use next
FAQ
How many centimetres are in an inch?
Exactly 2.54. The inch has been defined that way by international agreement since 1959, so a 12-inch ruler is precisely 30.48 cm.
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5 and add 32. So 20 °C is 20 × 9 ÷ 5 + 32 = 68 °F. To go back, subtract 32 and multiply by 5 ÷ 9.
How many pounds are in a kilogram?
About 2.2046. One pound is exactly 0.45359237 kg, so a kilogram is 1 ÷ 0.45359237 pounds.
Why does my 1 TB drive show about 931 GB?
Manufacturers use 1 TB = 10¹² bytes, while Windows divides by 1,024 repeatedly and labels the result GB. 10¹² bytes is 931.3 GiB, so no space is actually missing.
Is a UK gallon the same as a US gallon?
No. A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres, so the UK gallon is about 20% larger.