Unit converter
Length, weight, temperature, volume, area and speed, converted with exact factors.
Converters for each kind of unit
Each has its own page with tables of the conversions people look up most and the definitions behind them:
- Length converterCentimeters, inches, feet, meters, miles and more, converted exactly.
- Weight converterKilograms, pounds, ounces, stone and tons, converted exactly.
- Temperature converterCelsius, Fahrenheit, kelvin and Rankine, with the formula for each.
- Volume converterLiters, US and imperial gallons, cups, fluid ounces and spoons.
- Area converterSquare feet and meters, acres, hectares and square miles.
- Speed converterKilometers per hour, miles per hour, knots, meters and feet per second.
Where the numbers come from
The factors are the exact definitions published by the US National Institute of Standards and Technology (NIST Handbook 44 and Special Publication 811). Each unit is stored as an exact fraction of a metric unit, and conversions are done with whole-number arithmetic, so converting there and back always returns exactly what you typed.
Questions
Which conversions are exact?
All the factors are exact: the inch is defined as 2.54 cm, the pound as 0.45359237 kg, the US gallon as 231 cubic inches and the imperial gallon as 4.54609 liters, and every other unit here follows from those and the metric system. Results that end within 12 decimal places are shown in full; others are rounded to 10 significant digits and marked with ≈.
What’s the difference between US and imperial units?
Lengths and weights are the same in both (an inch, a foot, a pound). Volumes differ: the imperial gallon, pint and fluid ounce used in the UK are different sizes from the US ones, so the converter lists them separately.
Can I convert negative numbers?
Yes, though only temperatures usually need them. Temperatures below absolute zero (−273.15 °C or −459.67 °F) are reported as impossible rather than converted.
Does it convert currencies?
No. Exchange rates change every minute and would need a data feed, which would mean your browser contacting another site. Number Anvil only does conversions with fixed, published definitions.
Is anything I enter sent anywhere?
No. Conversions are worked out in your browser. The value and units appear in the page address only so you can bookmark or share them.
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- Length converterCentimeters, inches, feet, meters, miles and more.
- Weight converterKilograms, pounds, ounces, stone and more.
- Temperature converterCelsius, Fahrenheit, kelvin and Rankine.
- Volume converterLiters, US and imperial gallons, cups and spoons.
- Area converterSquare feet and meters, acres and hectares.
- Speed converterMiles and kilometers per hour, knots and more.