British-American differences
Although the British-American system is still common in everyday use in the UK and US, internationally and in university and research writing Système International or SI units are the norm.
Some approximate SI and British-American equivalents are given below, including non-SI units accepted for use with the International System. Note that British and American units also differ in some cases, as does the spelling of metre/meter and litre/liter etc.
| SI | British-American |
| 1 millimetre GB or millimeter US (mm) | 0.04 inches |
| 1 centimetre GB or centimeter US (cm) | 0.394 inches |
| 1 metre GB or meter US (m) | 3.281 feet or 1.094 yards |
| 1 kilometre GB or kilometer US (km) | 0.621 miles |
| 1 hectare (ha) | 2.471 acres |
| 1 litre GB or liter US (l, L) | 0.22 GB gallons or 0.264 US gallons |
| 1 gram (g) | 0.035 ounces |
| 1 kilogram (kg) | 2.205 pounds |
| British-American | SI |
| 1 inch (in or “) | 2.54 cm |
| 1 foot (ft or ‘) | 30.5 cm |
| 1 yard (yd) | 0.914 m |
| 1 mile | 1.609 km |
| 1 acre | 0.405 ha |
| 1 square mile | 2.6 km2 |
| 1 ounce (oz) | 28.35 g |
| 1 pound (lb) | 0.454 kg |
| 1 GB stone | 6.350 kg |
| 1 GB fluid ounce (fl. oz) | 28.41 ml |
| 1 US fluid ounce (fl. oz) | 29.57 ml |
| 1 GB pint | 0.568 L |
| 1 US pint | 0.473 L |
| 1 GB gallon | 4.546 L |
| 1 US gallon | 3.785 L |
| 1 foot | 12 inches |
| 1 yard | 3 feet |
| 1 pound | 16 ounces |
| 1 GB stone | 14 pounds |
| 1 GB pint | 20 GB fluid ounces |
| 1 US pint | 16 US fluid ounces |
| 1 quart | 2 pints |
| 1 gallon | 8 pints |
| 32 Fahrenheit | 0 Celsius |
| 212 Fahrenheit | 100 Celsius |