Why do US and UK gallons differ?

They are separate definitions that were never reconciled: a US gallon is 3.785 litres, a UK (imperial) gallon is 4.546 litres — about 20% larger. The same applies to pints and fluid ounces, which matters in recipes.

Are the conversion factors exact?

The key ones are exact by definition: 1 in = 2.54 cm, 1 lb = 0.45359237 kg, 1 mile = 1.609344 km. Results are rounded only for display.

Which is right, 'metres' or 'meters'?

Both — 'metre' is the international spelling, 'meter' the US one. They are the same unit.

15 free tools

Unit Converters

Convert length, weight, volume, area and temperature using the exact defined factors, so only the display is ever rounded. Free, no sign-up, works on a phone.

NewLength ConverterA tool to convert length between different unitsOpen NewWeight ConverterEasily convert weights between various units.Open NewArea CalculatorCalculate the area of various shapes easily.Open NewVolume CalculatorCalculate the area of various shapes easily.Open NewTemperature ConverterConvert between Celsius, Fahrenheit and Kelvin instantly, with the formula and a table of common temperatures.Open

Length Converter — quick conversions

Temperature Converter — quick conversions

Weight Converter — quick conversions

Volume Calculator — quick conversions

Ml to Oz

In short

Convert length, weight, area and volume between metric and imperial units. Key factors: 1 in = 2.54 cm, 1 kg = 2.20462 lb, 1 m² = 10.7639 ft², 1 US gal = 3.78541 L.

Overview

Metric and imperial units meet constantly: a recipe in cups, a height in feet, a parcel in pounds. These converters use the exact defined factors — 1 inch is exactly 2.54 cm, 1 pound is exactly 0.45359237 kg — so only the display is rounded.

Which one do you need?

Height and distance — millimetres to miles, including feet and inches
Weight — grams, kilograms, ounces, pounds and stones
Cooking and liquids — millilitres, litres, cups, pints and gallons — US and UK
Weather and ovens — Celsius, Fahrenheit and Kelvin
Rooms and land — square metres, square feet, acres and hectares

All 15 tools in this section are free, work on a phone, and keep what you type on your own device. Nothing is stored and there is no sign-up.

Unit Converters: frequently asked questions

Why do US and UK gallons differ?: They are separate definitions that were never reconciled: a US gallon is 3.785 litres, a UK (imperial) gallon is 4.546 litres — about 20% larger. The same applies to pints and fluid ounces, which matters in recipes.
Are the conversion factors exact?: The key ones are exact by definition: 1 in = 2.54 cm, 1 lb = 0.45359237 kg, 1 mile = 1.609344 km. Results are rounded only for display.
Which is right, 'metres' or 'meters'?: Both — 'metre' is the international spelling, 'meter' the US one. They are the same unit.