Foot-pound (ft⋅lbf)
The work done by a force of one pound-force over one foot: about 1.35582 joules. Used for torque and energy in US engineering and ballistics.
1 foot-pound = 1.355817948 joules (approximately).
About the foot-pound
Foot-pound hides a trap: the same words name two different things. As energy, a foot-pound is what a force of one pound-force transfers when it acts through a distance of one foot, about 1.355818 J. As torque, usually called the pound-foot, it is dimensionally the same but physically distinct, since energy is a scalar and torque is a vector, which is why careful writers specify foot-pound of energy or of torque.
The unit is tied to the early history of energy. In 1850 James Prescott Joule published a refined value of 772.692 foot-pounds of work per British thermal unit, which was the key figure in his demonstration that work converts to heat at a fixed rate. The same system defines the mechanical horsepower as 550 foot-pounds per second.
Today American ballistics is the best-known user. Muzzle energy of a bullet is commonly stated in foot-pounds, and a figure of about 7 kJ for an elephant gun, which is roughly 5,200 foot-pounds, shows the typical range for large rifle cartridges.
Sources: Wikipedia: Foot-pound (energy); Wikipedia: James Prescott Joule; Wikipedia: Orders of magnitude (energy)
Foot-pound conversion chart
1 foot-pound expressed in every other energy unit:
| Unit | 1 foot-pound |
|---|---|
| Joules | 1.355817948 |
| Kilojoules | 0.001355817948 |
| Watt-hours | 0.0003766160968 |
| Kilowatt-hours | 3.766160968×10⁻⁷ |
| British Thermal Units | 0.001285067463 |
| Calories | 0.3240482668 |
| Kilocalories | 0.0003240482668 |
| Megajoules | 0.000001355817948 |
| Gigajoules | 1.355817948×10⁻⁹ |
| Megawatt-hours | 3.766160968×10⁻¹⁰ |
| Millijoules | 1,355.817948 |
| Electronvolts | 8.462350028×10¹⁸ |
| Kiloelectronvolts | 8.462350028×10¹⁵ |
| Megaelectronvolts | 8,462,350,027,827 |
| Gigaelectronvolts | 8,462,350,028 |
| Tons Of TNT | 3.240482668×10⁻¹⁰ |
| Tonnes Of Oil Equivalent | 3.238315535×10⁻¹¹ |
| Therms | 1.285374295×10⁻⁸ |
| Quads | 1.285067463×10⁻¹⁸ |
| Ergs | 13,558,179.48 |
| Calories (IT) | 0.3238315535 |
| Kilogram-force Meters | 0.1382549544 |
| Horsepower-hours | 5.050505051×10⁻⁷ |
| Liter-atmospheres | 0.01338088279 |
More US & Imperial units
- British thermal unit (energy)
- horsepower-hour (energy)
- inch (length)
- foot (length)
- yard (length)
- mile (length)
- thou (length)
- league (length)
- furlong (length)
- chain (length)
- rod (length)
- link (length)
- hand (length)
- pound (weight & mass)
- ounce (weight & mass)
- grain (weight & mass)
Browse all energy units.