How to use the power converter
- Enter the figure in Value. The default is 100.
- Choose its unit in From, for example horsepower (mechanical) or BTU/h (IT).
- Choose the target unit in To. The answer shows at once, to 12 significant figures.
- Use the table under the result to read the same power in every unit, or swap From and To.
What it does and when to use it
Power is the rate of using or producing energy. Different trades count it in different units. Car makers quote engines in kW, hp or PS. Heating and air conditioning specs use BTU/h or tons. Electrical equipment uses watts and kilowatts, and physics books may use erg/s or ft·lbf/s.
Common jobs: comparing a European car’s PS with a US hp figure, checking whether a 9,000 BTU/h air conditioner suits a room, or turning a motor’s hp rating into kW for a wiring plan. To cost the electricity, take the kW figure to the electricity cost calculator. For energy totals (kWh, joules, BTU) rather than rates, use the energy converter.
How it works
Each unit is stored as watts. The tool multiplies by the From factor and divides by the To factor.
| Unit | Watts | Definition |
|---|---|---|
| horsepower (mechanical) | 745.699871582 | 550 ft·lbf/s |
| metric horsepower (PS) | 735.49875 | 75 kgf·m/s |
| electrical horsepower | 746 | defined |
| BTU/h (IT) | 0.293071070172 | 1,055.05585262 J per hour |
| kcal/h | 1.16222222222 | 4,184 J per hour |
| ft·lbf/s | 1.35581794833 | 0.3048 m × 4.4482216152605 N |
| ton of refrigeration | 3,516.85284207 | 12,000 BTU/h |
| erg/s | 0.0000001 | 10⁻⁷ W |
All factors come from exact definitions: the international foot and pound (1959), standard gravity 9.80665 m/s², the IT BTU and the thermochemical calorie. They match NIST’s Appendix B.8 to the digits NIST prints.
Worked examples
Metric horsepower. 150 PS = 110.3248125 kilowatts, which is 147.948010593 hp (mechanical).
A room air conditioner. 9,000 BTU/h = 2,637.63963155 watts, or 0.75 tons of refrigeration.
A 2-ton split system. 2 tons = 7.03370568413 kilowatts of cooling, which is 24,000 BTU/h.
Limits and tips
- Cooling output is not power drawn. An air conditioner moves more heat than the electricity it uses. The ratio is its efficiency rating (COP or EER), which this converter does not know.
- Engine figures depend on how they were measured. Brake hp, wheel hp and different test standards give different numbers for the same engine. The converter only changes the unit.
- To find motor current from power and voltage, use the Ohm’s law calculator.
Frequently asked questions
What is the difference between hp and PS?
How many BTU/h is 1 kW?
What is a ton of refrigeration?
What is electrical horsepower?
Why does my kcal/h result differ from another calculator?
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically — NIST, accessed 2026-10-08
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