Power Converter
Convert power between watts, kilowatts, megawatts, mechanical, metric and electrical horsepower, BTU per hour and tons of refrigeration.
Updated Formula covered by automated tests
Power is how fast energy is delivered or used, and the same quantity hides behind very different labels: kilowatts on a European car brochure, horsepower on an American one, PS on a German spec sheet, BTU per hour on an air conditioner box and tons on a commercial chiller. This converter takes a value in any of those units and shows it in all the others at once, using the exact definitions published by NIST.
Typical uses are comparing engine ratings across markets, sizing a generator or inverter for appliances listed in watts, checking whether a heat pump rated in BTU/h matches a kilowatt heat-loss estimate, or translating a motor nameplate. Because three different horsepowers are still in use, the tool lists mechanical, metric and electrical horsepower separately rather than pretending they are the same.
The formula
- P (W)
- The power expressed in watts, the SI unit equal to one joule per second
- factor
- How many watts one of the chosen unit contains, for example 1000 for kilowatts
- ft·lbf/s
- Foot-pound-force per second: lifting one pound one foot each second
- kgf·m/s
- Kilogram-force meter per second: lifting one kilogram one meter each second under standard gravity
- BTU/h
- International Table British thermal units per hour; 1 BTU is 1055.05585262 J
James Watt needed a way to sell steam engines to mine owners who measured work in horses. He settled on 33,000 foot-pounds per minute (550 per second) for one horse, a deliberately generous figure. Once the foot was fixed at 0.3048 m and the pound-force at 4.4482216152605 N, mechanical horsepower became exactly 745.69987158227022 W. Continental Europe redefined the horse with metric units as 75 kilogram-force meters per second, which gives the slightly smaller metric horsepower (PS, CV or ch) of exactly 735.49875 W.
Electrical horsepower, used on some motor nameplates, was simply rounded to 746 W. The refrigeration ton comes from the ice trade: melting one short ton of ice in 24 hours absorbs about 288,000 BTU, or 12,000 BTU per hour. All conversions here pass through watts, so every pair of units is consistent with every other.
Worked example
Lukas is comparing two versions of the same hatchback. The German brochure quotes 150 kW, while a US review lists the engine in horsepower and a British magazine in PS. He wants all three on the same footing.
- 1 Convert to watts: 150 kW × 1000 = 150,000 W.
- 2 Mechanical horsepower: 150,000 ÷ 745.69987 = 201.15 hp.
- 3 Metric horsepower: 150,000 ÷ 735.49875 = 203.94 PS.
- 4 For comparison, electrical horsepower: 150,000 ÷ 746 = 201.07 hp(E).
Result: The engine makes about 201 hp in US terms and about 204 PS in European terms, so the two reviews describe the same engine even though the numbers differ by almost 3 units.
Before you rely on the result
- This tool converts units only. It does not account for efficiency, so a 1 kW electric heater and a 1 kW motor draw the same electrical power but deliver different useful output.
- Engine ratings depend on the test standard (SAE J1349, DIN 70020, ECE R85) and on whether the figure is measured at the crankshaft or the wheels; converting units cannot reconcile different test methods.
Frequently asked questions
Why does a car have more PS than hp?
One PS is about 1.4 percent smaller than one mechanical horsepower (735.5 W versus 745.7 W), so the same output produces a larger number in PS. A 100 kW engine is 134.1 hp or 136.0 PS.
How do I size an air conditioner in BTU/h from watts of cooling?
Divide the cooling output in watts by 0.29307 to get BTU/h. A unit that removes 3.5 kW of heat is about 11,940 BTU/h, roughly one refrigeration ton. Note that this is cooling capacity, not the electrical power the unit draws, which is usually a third or less of that figure.
Is a kilowatt the same as a kilowatt-hour?
No. A kilowatt is a rate; a kilowatt-hour is an amount of energy, the energy used by a 1 kW load running for one hour. Your electricity bill counts kilowatt-hours, while an appliance label states kilowatts.
Which horsepower should I use for an electric motor?
In the United States, motor nameplates use mechanical horsepower for shaft output, and 746 W is a common rounded equivalent. In Europe, motors are rated in kilowatts. If a motor is labeled only "HP", the difference between 745.7 and 746 W is far smaller than motor efficiency losses.