Guides / Units

Metric and Imperial Conversions Explained

Most of the world uses metric units. The United States and a few other countries still use imperial units for everyday measurements. Knowing the exact conversion factors saves guesswork when you travel, shop online or follow a recipe.

Length

The key figure is that one inch is exactly 2.54 centimetres. Everything else follows from that:

• 1 foot = 12 inches = 30.48 cm
• 1 yard = 3 feet = 0.9144 m
• 1 mile = 1,760 yards = 1.609344 km

A quick estimate: 1 mile is roughly 1.6 km, and 1 km is roughly 0.62 miles.

Weight

One pound is exactly 0.45359237 kilograms, and one ounce is one sixteenth of a pound. A stone, used mostly for body weight in the UK, is 14 pounds, or about 6.35 kg.

For quick estimates, 1 kg is about 2.2 pounds. A 70 kg person weighs about 154 pounds.

Temperature

Temperature does not scale in a straight line like length or weight, so it needs a formula:

• Celsius to Fahrenheit: multiply by 9/5, then add 32.
• Fahrenheit to Celsius: subtract 32, then multiply by 5/9.
• Celsius to Kelvin: add 273.15.

Water freezes at 0 °C, which is 32 °F, and boils at 100 °C, which is 212 °F. For an oven or a fever, these formulas are the ones to use.

Try it yourself

The Unit Converter handles length, weight and temperature. Type a value in either box and the other one updates.