Unit converter

Converting between metric and imperial units comes up constantly: reading a recipe, ordering materials, comparing product specifications or travelling abroad. This converter handles length, mass, volume and speed using exact base-unit factors, so results are precise.

How to use it

1. Choose the category: length, mass, volume or speed.
2. Choose the source and target units.
3. Enter a value and read the result.

How it works

Each unit is defined by its factor relative to a base unit (metre, kilogram, litre, metre per second). The value is converted to the base unit and then to the target. Several factors are exact by definition: 1 inch = 2.54 cm exactly, and 1 pound = 0.45359237 kg exactly.

Common conversions

• 1 mile = 1.609344 km; 1 km = 0.621371 miles
• 1 foot = 0.3048 m; 1 m = 3.28084 ft
• 1 kg = 2.20462 lb; 1 lb = 453.592 g
• 1 US gallon = 3.78541 L; 1 imperial gallon = 4.54609 L
• 100 km/h = 62.14 mph; 1 knot = 1.852 km/h

Worked example

A 5 ft 11 in person is (5 × 12 + 11) × 2.54 = 71 × 2.54 = 180.3 cm. A 25 kg suitcase weighs 25 × 2.20462 = 55.1 lb.

Watch out for

• US vs. imperial volumes: US gallons, quarts, pints and fluid ounces are smaller than British imperial ones.
• Short ton vs. long ton vs. tonne: 2,000 lb, 2,240 lb and 1,000 kg respectively.
• Rounding: keep full precision through calculations and round only the final result.