π Power Converter
Watts, kilowatts, horsepower, and BTU/h with live conversion.
All power units
How to Use This Power Converter
Enter a power value, choose its unit, and see every equivalent instantly. Car shoppers compare horsepower across US and European specs, homeowners size generators and air conditioners, and engineers convert between electrical and mechanical power daily.
Type the power value.
Pick the starting unit, watching which horsepower definition applies.
Read all converted units in the results panel.
Power Units Explained
The watt is the SI unit: one joule per second. A 100-watt bulb converts 100 joules of electrical energy into light and heat every second. Horsepower predates electricity: James Watt defined it around 1780 to market steam engines to mine owners who knew what a horse could do. One mechanical horsepower equals 745.7 watts by definition.
Three horsepower definitions survive because different industries standardized separately. Mechanical (imperial) horsepower at 745.7 W is the US automotive standard. Metric horsepower (PS, PferdestΓ€rke) at 735.5 W is the European automotive standard, which is why a "300 PS" European car is about 296 US hp. Electrical horsepower at exactly 746 W is used for electric motors. BTU per hour dominates US HVAC: a "12,000 BTU" air conditioner moves heat at about 3.5 kW.
Key Conversion Factors
Worked Example
A European car is rated 150 PS. In US mechanical horsepower: 150 Γ 735.5 Γ· 745.7 = 147.9 hp, about a 1.4 percent haircut. An air conditioner rated 12,000 BTU/h draws the equivalent of 12,000 Γ 0.2931 = 3,517 watts of cooling power, though its electrical consumption is far less thanks to the refrigeration cycle's efficiency.
Practical Context
A typical US home's peak electrical draw is 5 to 10 kW. A portable generator rated 7,500 watts can run essentials but not central air. EV motors are increasingly rated in kW (a 150 kW motor is about 201 hp), and the industry is slowly abandoning horsepower for the cleaner SI unit. When comparing, always convert to watts first: it is the one unit everyone agrees on.
Power vs Energy: Do Not Confuse Them
Power is the rate of using energy; energy is the total amount. A 100-watt bulb run for 10 hours uses 1,000 watt-hours (1 kWh) of energy. Your electricity bill charges for energy (kWh), while circuit breakers and wire gauges care about power (watts or amps). Mixing them up is the most common mistake in home electrical projects: a generator rated 5,000 watts can run a 1,500-watt heater easily, but only for as long as its fuel provides the total energy needed.
Frequently Asked Questions
How many watts are in one horsepower?
745.7 watts for mechanical (US) horsepower, 735.5 watts for metric horsepower (PS), and exactly 746 watts for electrical horsepower. The differences come from separate historical definitions.
What is the difference between HP and PS?
HP usually means mechanical horsepower (745.7 W, the US auto standard). PS (PferdestΓ€rke) is metric horsepower (735.5 W, the European standard). A 300 PS European engine is about 296 US hp.
How do I convert BTU to watts?
Multiply BTU/h by 0.2931 to get watts. A 12,000 BTU/h air conditioner equals about 3,517 watts of cooling capacity.
Is horsepower still used for electric cars?
Decreasingly. EVs are increasingly rated in kilowatts (the SI unit), though marketing still quotes hp equivalents because buyers understand them. A 150 kW motor is about 201 hp.
What does 1 kW mean in practical terms?
One kilowatt runs ten 100-watt bulbs, or a typical microwave. US homes bill electricity in kilowatt-hours (kW Γ hours), and rooftop solar is sized in kW of peak output.