About the Horsepower Calculator
Horsepower measures how quickly an engine can do work, and torque is the twisting force it produces. The two are linked by engine speed: horsepower equals torque in pound-feet times rpm divided by 5,252. This horsepower calculator works from torque and rpm, or from a power figure, and shows the result in mechanical horsepower, metric horsepower (PS, CV or hk) and kilowatts. If you give an rpm with a power figure, it also tells you the torque at that speed. A drivetrain loss setting estimates the power that actually reaches the wheels.
Updated October 2026
How to use the Horsepower Calculator
- 1Choose whether you know torque and rpm, or power.
- 2For torque, enter the value, choose lb-ft or N·m, and enter the engine speed.
- 3For power, enter the value and choose hp, PS or kW.
- 4Enter a drivetrain loss percentage to estimate wheel power.
- 5Read the engine power in hp, PS and kW, and the wheel figure.
Formulas used
- hp = torque (lb-ft) × rpm ÷ 5,252
- Power (W) = torque (N·m) × 2π × rpm ÷ 60
- 1 hp = 745.7 W; 1 PS = 735.5 W; 1 kW = 1.341 hp
- 1 lb-ft = 1.3558 N·m
- Wheel power = engine power × (1 − loss percentage)
Using the loss figure
If a dyno test shows 255 wheel horsepower and you want to estimate the engine figure, divide by (1 minus the loss). With a 15 percent loss, 255 divided by 0.85 gives 300 hp at the crank. The reverse works too: enter your engine power and loss percentage to estimate what a dyno should show. Treat these as estimates because actual losses vary with the vehicle and conditions.
More power and energy tools
The Power Converter handles watts, kilowatts and horsepower in bulk, the Energy Converter covers joules and kilowatt-hours, and the Fuel Economy Calculator relates power to efficiency. For electrical equipment, use the Watts, Amps and Volts Calculator. A power number alone does not tell you how a vehicle will perform, since weight, gearing and tyres also matter.
Features
- Horsepower from torque and rpm
- hp, PS (metric hp) and kW conversions
- Torque at a chosen rpm from a power figure
- Wheel horsepower with adjustable loss
- Torque in lb-ft or N·m
- Exact standard conversion factors
- Runs in your browser
Frequently asked questions
How do you calculate horsepower from torque?
Multiply torque in pound-feet by rpm and divide by 5,252. An engine making 300 lb-ft at 5,252 rpm produces 300 hp. At 3,000 rpm the same torque gives 300 times 3,000 divided by 5,252, which is about 171 hp. The two curves always cross at 5,252 rpm.
What is the difference between hp and PS?
Mechanical horsepower (hp) is 745.7 watts, used in the US and UK. Metric horsepower is 735.5 watts and is written PS in Germany, CV in France and Italy, and hk in Scandinavia. A 100 PS engine is therefore about 98.6 hp. Always check which is used when comparing cars from different countries.
How do I convert hp to kW?
Multiply horsepower by 0.7457 to get kilowatts, or kilowatts by 1.341 to get horsepower. A 150 hp engine makes about 112 kW. The tool shows all three units together.
What is wheel horsepower?
Wheel horsepower is the power that actually reaches the driving wheels, measured on a chassis dynamometer. It is lower than engine (crank) power because the gearbox, driveshaft, differential and tyres absorb some. Losses of about 10 to 15 percent for manual cars and 15 to 20 percent or more for automatics and four-wheel drive are typical.
Why does torque matter as much as horsepower?
Torque is what accelerates the car, and horsepower is torque multiplied by how fast the engine spins. An engine with broad, strong torque feels punchy at low rpm, while a high-revving engine can make the same horsepower with less torque at higher speeds. Looking at both tells you more than either alone.
Are the results exact?
The conversions use exact standard definitions. Real-world horsepower figures from dynamometers vary with temperature, air pressure, correction standards and the equipment used, so numbers from different sources are not always comparable.