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Approximate conversion factors
The table below lists quick "rules of thumb" that may jog your memory. They are not accurate conversion factors, but rather approximate values for doing quick calculations that don't require strict accuracy.
| Customary Unit | Approximate Metric Values (Do not use as conversion factors) |
|---|---|
| acre | 4000 square meters or 0.4 hectare |
| barrel | 0.16 cubic meter |
| British thermal unit | 1000 joules |
| British thermal unit per pound-mass | 2300 joules per kilogram or 2.3 kilojoules per kilogram |
| calorie | 4 joules |
| centipoise | 1* millipascal-second |
| centistokes | 1* square millimeter per second |
| darcy | 1 square micrometer |
| degree Fahrenheit (temperature difference) | 0.5 Kelvin |
| dyne per centimeter | 1* millinewton per meter |
| foot | 30 centimeters or 0.3 meter |
| cubic foot (cu ft) | 0.03 cubic meter |
| cubic foot per pound-mass (ft3/lbm) | 0.06 cubic meter per kilogram |
| square foot (sq ft) | 0.1 square meter |
| foot per minute | 0.3 meter per minute or 5 millimeters per second |
| foot-pound-force | 1.4 joules |
| foot-pound-force per minute | 0.02 watt |
| foot-pound-force per second | 1.4 watts |
| horsepower | 750 watts (¾ kilowatt) |
| horsepower, boiler | 10 kilowatts |
| inch | 2.5 centimeters |
| kilowatt-hour | 3.6* megajoules |
| mile | 1.6 kilometers |
| ounce (avoirdupois) | 28 grams |
| ounce (fluid) | 30 cubic centimeters |
| pound-force | 4.5 newtons |
| pound-force per square inch (pressure, psi) | 7 kilopascals |
| pound-mass | 0.5 kilogram |
| pound-mass per cubic foot | 16 kilograms per cubic meter |
| section | 260 hectares or 2.6 million square meters or |
| ton, long (2240 pounds-mass) | 1000 kilograms |
| ton, metric (tonne) | 1000* kilograms |
| ton, short | 900 kilograms |
*Exact equivalents