Watt-hours to Foot-pounds (Wh to ft⋅lbf)

1 watt-hour equals 2,655.223737 foot-pounds (rounded).

1 watt-hour = 2,655.223737 foot-pounds

How to convert watt-hours to foot-pounds

To convert watt-hours to foot-pounds, multiply the number of watt-hours by 2,655.223737. The factor is rounded to 10 significant digits. To go the other way, multiply foot-pounds by 0.0003766160968 (rounded).

foot-pounds = watt-hours × 2,655.223737

Example: 10 watt-hours = 26,552.23737 foot-pounds.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Watt-hour (Wh)

Metric (SI)Current unit

Exactly 3,600 joules, the energy used by a one-watt device in an hour. Battery capacities are quoted in watt-hours.

Pair a power unit with a unit of time and you get the watt-hour: one watt sustained for one hour, which works out to 3,600 joules. The watt itself was adopted at the second International Electrical Congress in 1889, in the same session that adopted the joule, so the two units share a birthday even though the watt-hour is the one people read off batteries.

Battery capacity is where it earns its keep. Multiplying amp-hours by the battery voltage gives an estimate of watt-hours, so a 2,500 mAh lithium-ion cell at 3.7 V holds roughly 9.25 Wh. That is why a 500 mA USB device runs about 3.7 hours on it rather than five: the cell voltage, not the 5 V from the port, sets the energy.

For scale, an alkaline AA battery holds about 9 kJ, which is 2.5 Wh. A 12 W LED lamp left on for an hour uses 12 Wh, and a 40 W appliance running for 25 hours uses 1,000 Wh.

1 watt-hour = 3,600 joules (exactly).

Sources: Wikipedia: Watt-hour; Wikipedia: Joule; Wikipedia: Orders of magnitude (energy)

Foot-pound (ft⋅lbf)

US & ImperialCurrent unit

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.

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.

1 foot-pound = 1.355817948 joules (approximately).

Sources: Wikipedia: Foot-pound (energy); Wikipedia: James Prescott Joule; Wikipedia: Orders of magnitude (energy)

Related conversions

See all energy units.