Metric vs Imperial: A Unit Conversion Cheat Sheet
Most of the world uses the metric system, while the United States relies mainly on customary units and the United Kingdom mixes both. If you cook from foreign recipes, travel, shop online or read technical documents, you will need to switch between them. Here are the conversions people use most, plus simple tricks for doing them in your head. For anything more precise, use the Unit Converter.
Length
| Imperial | Metric |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 0.3048 m |
| 1 yard | 0.9144 m |
| 1 mile | 1.609 km |
Mental trick: a kilometre is about 0.6 of a mile. To turn miles into kilometres, multiply by 1.6. Our Length Converter handles the exact numbers. A person who is 6 ft 2 in tall is 74 inches × 2.54 = 187.96 cm.
Weight and mass
| Imperial | Metric |
|---|---|
| 1 ounce | 28.35 g |
| 1 pound | 0.4536 kg |
| 1 stone (14 lb) | 6.35 kg |
Mental trick: one kilogram is about 2.2 pounds. Halve the pounds and subtract 10 percent to get kilograms roughly. Try the Weight Converter for exact results.
Volume and cooking
| US measure | Metric |
|---|---|
| 1 teaspoon | about 5 mL |
| 1 tablespoon | about 15 mL |
| 1 fluid ounce | 29.57 mL |
| 1 cup | 236.6 mL |
| 1 pint | 473 mL |
| 1 US gallon | 3.785 L |
Beware: an imperial (UK) gallon is 4.546 litres, about 20 percent larger than a US gallon, and an imperial pint is 568 mL. When a recipe or fuel figure comes from the UK, check which system it uses. The Volume Converter covers both.
Temperature
Temperature does not convert with a simple multiplier because the two scales start at different points.
- Celsius to Fahrenheit: multiply by 9/5 and add 32.
- Fahrenheit to Celsius: subtract 32 and multiply by 5/9.
- Celsius to Kelvin: add 273.15.
| °C | °F | What it feels like |
|---|---|---|
| 0 | 32 | Water freezes |
| 20 | 68 | Comfortable room temperature |
| 37 | 98.6 | Normal body temperature |
| 100 | 212 | Water boils |
Mental trick: double the Celsius value and add 30 for a rough Fahrenheit figure. Use the Temperature Converter for exact values.
Speed
| From | To | Multiply by |
|---|---|---|
| mph | km/h | 1.609 |
| km/h | m/s | 0.2778 (divide by 3.6) |
| knots | km/h | 1.852 |
So 60 mph is about 96.6 km/h, and 100 km/h is about 62 mph. See the Speed Converter.
Area
An acre is 4,046.86 square metres (43,560 square feet) and a hectare is 10,000 square metres, so one hectare is about 2.47 acres. Remember that area conversion factors are the length factor squared: 1 m is 3.28 ft, but 1 m² is 10.76 ft². Use the Area Converter for land and room sizes.
Common conversion mistakes
- Mixing US and imperial gallons, pints and fluid ounces.
- Converting area with the length factor instead of squaring it.
- Rounding too early in a multi-step calculation.
- Confusing weight (a force) with mass in science problems.
- Forgetting units when copying numbers between documents.
Keep this page handy
Bookmark this cheat sheet for quick reference, and use the converters whenever you need more decimal places or unusual units.