Power Converter
Enter a power, pick the unit it is in and the unit you want. The result, the factor between the two units and the same power in every supported unit are shown.
Converted power
745.699872 W
Conversion factor
745.6998715823 W per hp
How it works
Every power unit is defined as some number of watts (joules per second). The calculator multiplies your value by the size of the unit it is in to get watts, then divides by the size of the unit you want.
Mechanical horsepower is 550 foot-pounds per second; with the exact pound-force and foot that is 745.69987 W. Metric horsepower (PS, from the German Pferdestärke) is 75 kgf·m/s, exactly 735.49875 W, about 1.4% smaller. BTU per hour divides the International Table BTU by 3,600 s, and a ton of refrigeration is 12,000 BTU/h, the rate at which a short ton of ice melts in a day.
The conversion factor is what one unit of the 'from' unit is worth in the 'to' unit, so you can apply it to other ratings by hand. The table lists the same power in every unit the converter knows.
Formula
watts = value × (size of the from unit in W) converted = watts ÷ (size of the to unit in W) factor = size of from unit ÷ size of to unit 1 hp = 550 × 4.4482216152605 × 0.3048 1 PS = 735.49875 1 BTU/h = 1,055.05585262 / 3,600 1 ton of refrigeration = 12,000 BTU/h 1 ft·lbf/s = 4.4482216152605 × 0.3048
Example
1 hp, the default, is 550 × 1.3558179483 = 745.699872 W. The factor from hp to W is 745.6998715823, so a 200 hp engine is 149.14 kW.
The table shows the same horsepower as 0.7457 kW, 1.01387 PS, 2,544.433578 BTU/h, 0.212036 tons of refrigeration and 550 ft·lbf/s. A 3-ton air conditioner is 36,000 BTU/h, which is 3 × 3,516.852842 = 10,550.558526 W, or 10.550559 kW.
Assumptions and limitations
- Horsepower (hp) is mechanical horsepower, 550 ft·lbf/s = 745.69987158 W. Electrical horsepower (746 W exactly) and boiler horsepower (about 9.81 kW) are different units and are not offered.
- PS is metric horsepower, 75 kgf·m/s = 735.49875 W exactly (DIN 66036). The French ch and Italian CV are the same unit.
- BTU/h and tons of refrigeration use the International Table BTU (1,055.05585262 J). A ton of refrigeration is exactly 12,000 BTU/h = 3,516.852842 W.
- A negative value is converted as entered, which is useful for power absorbed rather than delivered.
- Results are shown to six decimal places; very small values may display as 0 even though the conversion is computed in full precision.
Frequently asked questions
Why are hp and PS different?
They come from different definitions. Mechanical hp is 550 ft·lbf/s (745.70 W); metric PS is 75 kgf·m/s (735.50 W). A car rated at 300 PS has about 296 hp, so the two figures in a brochure are not a mistake.
How many watts is a ton of air conditioning?
A ton of refrigeration is 12,000 BTU/h, which is 3,516.85 W of cooling. That is the heat removed, not the electrical power drawn; a typical air conditioner draws roughly a quarter to a third of that as electricity.
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