Convert Units Fast: Free Online Unit Converter

Every conversion uses the exact internationally defined factors, such as 1 pound = 0.45359237 kilograms and 1 inch = 2.54 centimeters. Nothing is approximated at the source. The only rounding happens when results are displayed, and the full precision is used internally.

US. One US fluid ounce is exactly 29.5735295625 milliliters. The UK imperial fluid ounce is smaller at 28.4130625 milliliters, so recipes and labels from different countries are not interchangeable. This site always uses the US fluid ounce.

US. One US gallon is exactly 3.785411784 liters. The imperial gallon used in the UK is larger at 4.54609 liters. Fuel figures and liquid volumes differ between the two systems, so check which gallon your source means.

Because since 1959 the pound has been defined as exactly 0.45359237 kilograms. Dividing 1 by 0.45359237 gives 2.2046226218 and so on, which is why 2.20462 gets quoted so often. This converter uses the full definition, not the rounded shortcut.

Yes. Since 1959 the international inch has been defined as exactly 2.54 centimeters, with no rounding involved. Older survey inches differed very slightly, but they are obsolete for everyday and engineering use.

Kelvin and Celsius degrees are the same size; the scales are simply offset. To go from Celsius to kelvin you add 273.15, and to go from kelvin to Celsius you subtract 273.15. Fahrenheit uses a different degree size, so it converts through Celsius with the formula °F = °C × 9/5 + 32.

Results are shown with up to 4 decimal places and trailing zeros are trimmed, so 2.5000 displays as 2.5. The conversion itself is computed at full precision first, so rounding only affects what you see, not the underlying math.

Yes, it is completely free and there is no signup, account, or app to install. All calculations run in your browser with plain JavaScript, so nothing you type is sent to a server.