Metric to Imperial Conversions: A Practical Cheat Sheet

Most of the world uses the metric system, while the United States and a few other places still use imperial or US customary units. If you travel, cook from international recipes, buy products online or study science, you will need to convert between them. This cheat sheet gives the exact factors, worked examples and a few easy mental shortcuts.

Length

• 1 inch = 2.54 centimetres (exactly).
• 1 foot = 0.3048 metres (exactly), or 30.48 cm.
• 1 yard = 0.9144 metres.
• 1 mile = 1.609344 kilometres.
• 1 kilometre = 0.621371 miles.

Example: a height of 5 feet 9 inches is 69 inches, and 69 × 2.54 = 175.26 cm. A marathon is 42.195 km, which is about 26.2 miles.

Shortcut: to convert kilometres to miles, multiply by 0.6 for a quick estimate (100 km is about 60 miles; the exact figure is 62.1).

Weight and Mass

• 1 pound = 0.45359237 kilograms (exactly).
• 1 kilogram = 2.20462 pounds.
• 1 ounce = 28.3495 grams.
• 1 stone = 14 pounds = 6.35029 kilograms.

Example: 180 pounds is 180 × 0.45359237 = 81.65 kg. A 70 kg person weighs about 154.3 pounds, or 11 stone.

Shortcut: halve a weight in pounds and subtract about 10% to estimate kilograms.

Volume

• 1 US gallon = 3.785411784 litres.
• 1 imperial (UK) gallon = 4.54609 litres.
• 1 US fluid ounce = 29.5735 millilitres; 1 imperial fluid ounce = 28.4131 millilitres.
• 1 US liquid pint = 473.176 millilitres; 1 imperial pint = 568.261 millilitres.

Watch out for the US and UK differences: a UK gallon is about 20% bigger than a US gallon, and a UK pint is bigger than a US pint. This matters for fuel economy figures: miles per gallon in the UK and the US are not directly comparable.

Kitchen Measures

• 1 US cup = 236.588 millilitres, while a metric cup used in Australia, New Zealand and many recipes is 250 millilitres.
• 1 US tablespoon = 14.787 millilitres, and 1 teaspoon = 4.929 millilitres. In many countries, a metric tablespoon is 15 ml and a teaspoon is 5 ml (Australia uses a 20 ml tablespoon).
• For baking, weigh ingredients in grams where possible, since cups vary with how tightly an ingredient is packed.

Temperature

• Fahrenheit = Celsius × 9 ÷ 5 + 32.
• Celsius = (Fahrenheit − 32) × 5 ÷ 9.
• Kelvin = Celsius + 273.15.

Example: an oven set to 350 °F is (350 − 32) × 5 ÷ 9 = 176.7 °C, usually rounded to 175 or 180 °C. Normal body temperature of 37 °C is 98.6 °F. Water freezes at 0 °C or 32 °F and boils at 100 °C or 212 °F at sea level.

Shortcut: to estimate Fahrenheit from Celsius, double it and add 30. For 20 °C that gives 70 °F, close to the exact 68 °F, and accurate enough for weather.

Speed

• 1 mile per hour = 1.609344 kilometres per hour.
• 100 km/h = 62.14 mph; 60 mph = 96.56 km/h.
• 1 knot = 1.852 km/h, which is 1 nautical mile per hour.

Area

• 1 square foot = 0.092903 square metres.
• 1 acre = 4,046.86 square metres = 0.404686 hectares.
• 1 hectare = 2.47105 acres.

Tips for Accurate Conversions

• Convert only at the end of a calculation, and keep extra decimal places until then.
• Check which version of a unit is used: US or imperial gallons, short or metric tons, US or metric cups.
• Make sure all values in a formula use the same system. Mixing units has caused expensive mistakes: in 1999, NASA lost the Mars Climate Orbiter spacecraft after one team's software used pound-force seconds while another expected newton-seconds.
• For anything involving health, medicine or safety, double-check conversions or use a trusted tool.

Related Guides

Percentages and unit conversions often go hand in hand in everyday calculations. See our guide to calculating percentages, and our guide to BMI, which can be calculated in metric or imperial units.

Three habits

Keep the exact factors for the units you use most, convert only at the end, and write the unit next to every number. For quick estimates: kilometres × 0.6 is roughly miles, and Celsius × 2 + 30 is roughly Fahrenheit.