Unit & Measurement Converter

Pick the category first, then the unit you have and the unit you want — the conversion happens as you type. The definitions are exact rather than approximate: an inch is exactly 25.4 millimetres, a pound is exactly 0.45359237 kilograms, and a mile is exactly 1,609.344 metres. Those are not rounded values, they are the legal definitions, which is why a good free online converter and a reference table always agree to the last decimal. The table under the result shows the same value in every other unit of that category, which is usually faster than converting twice.

Because temperature scales do not start at the same place. Length is a ratio scale: zero metres and zero feet are the same point, so you convert by multiplying. Celsius and Fahrenheit have different zero points, so 20 °C is not "twice" 10 °C in any meaningful sense and you cannot convert by multiplying alone. The tool applies the proper formula (°F = °C × 9/5 + 32, K = °C + 273.15). It is also why converting a temperature difference is not the same as converting a temperature: a rise of 10 °C is a rise of 18 °F, not 50 °F.

No, and it is the most common conversion error there is. A US gallon is about 3.785 litres, an imperial (UK) gallon about 4.546 — roughly 20 per cent bigger. The same split applies to pints, quarts and fluid ounces, and to make it worse a US fluid ounce is slightly larger than a UK one while a US pint is smaller. This converter uses US definitions throughout. If you are following a British recipe or reading a fuel-economy figure from the UK, convert the units knowingly rather than assuming a "pint" is a pint.