Informal conversion of common units
Informal conversion of common measuring units often needs to be done without calculator or computer. This article is an informal listing of some quick and dirty conversions between the system used in the United States and metric or SI units. When people say "a foot long" or "ten kilometers from here", they rarely mean ".3048 m" or "6.21571 miles".
These are all rough approximations; for more accurate information, see Conversion of units.
1° (degree) |
100 km |
70 statute miles |
60 nautical miles |
1′ (minute) |
2 km |
1 nautical mile |
|
1″ (second) |
30 m |
5 cm |
2 inches (in.) |
3 cm |
1 in. |
10 cm |
4 in. |
30 cm |
1 foot (ft.) |
1 m |
3 ft. |
1 m |
1 yard |
200 m |
1 furlong |
2 km |
1 mile |
5 km |
3 miles |
8 km |
5 miles |
1 m² |
10 ft² |
4000 m² |
1 acre |
2 ha |
5 acres |
1 km² |
250 acres |
5 km² |
2 square miles |
1 L |
2 pints |
4 L |
1 gallon (gal.) |
6 US gallons |
5 Imperial gallons |
160 L |
1 barrel |
30 g |
1 ounce (oz.) |
200 g |
7 oz. |
½ kg |
1 pound (lb.) |
1 kg |
2 lb. |
50 kg |
1 hundredweight (cwt.) |
1 t |
1 ton |
1 km/h |
0.3 m/s |
1 foot per second (ft/s) |
2 km/h |
½ m/s |
1 knot |
3 km/h |
1 m/s |
2 miles per hour (mph) |
3 N |
20 poundal |
5 N |
1 pound-force (lbf) |
1 bar = 1000 hPa |
1 atm |
15 psi |
4 mbar = 4 hPa |
3 torr = 3 mmHg |
|
100 mbar = 10 kPa |
3 inch mercury |
4 J |
1 calorie |
1 kJ |
1 British thermal unit |
3 kW |
4 horsepower |
Temperatures:
- Fahrenheit to Celsius -- subtract 30 and divide by 2
- Celsius to Fahrenheit -- multiply by 2 add 25
More accurate conversions
The following conversions can be done in your head with a little practice and are good to about 1%:
- A meter is 10% more than a yard
- A liter is 5% more than a U.S. quart
- A kilogram is 10% more than two pounds
See also
- Metrified Imperial system