Horsepower Calculator (HP from Torque and RPM)
How do you calculate horsepower from torque? Pick what to solve for, then enter the other two values: hp from torque and rpm, or the torque or rpm that gives a target power. The calculator uses exact constants and shows hp, kW and metric PS together. It answers "how much power"; for torque from a wrench force or lever arm, or the torque a given hp makes, use the torque calculator.
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Formula
hp = torque (lb-ft) x rpm / 5252power (W) = torque (N·m) x 2 x pi x rpm / 60torque = power / (2 x pi x rpm / 60);rpm = power / torque x 60 / (2 x pi)1 hp = 745.69987 W,1 PS = 735.49875 W,1 lb-ft = 1.3558179 N·m
The constant 5252 is 33,000 / (2 x pi) rounded; the calculator uses the unrounded value.
Worked example
300 lb-ft at 5000 rpm: 300 x 1.3558179 = 406.75 N·m, and 5000 rpm = 523.6 rad/s, so power = 406.75 x 523.6 = 212,971 W = 212.97 kW = 285.6 hp = 289.56 PS. The shortcut 300 x 5000 / 5252 gives 285.6 hp as well.
Metric example: 400 N·m at 6000 rpm is 251.33 kW, or 337.04 hp.
Horsepower vs torque
Torque is the twisting force the engine makes; horsepower is how fast it can deliver that work, torque times rpm. Torque tells you about pull at a given rpm, horsepower tells you about how hard the car keeps pulling as rpm rises. Use this page when you know torque and rpm and want power. Use the torque calculator when you want torque from a lever and force, or the torque implied by a power figure.
Typical values
Family cars typically make roughly 100 to 200 hp, and sports cars often 300 hp or more. Peak torque and peak power come at different rpm, so quote both rpm values.
Common mistakes
- Mixing torque units: lb-ft and N·m differ by a factor of 1.356.
- Using peak torque with peak-power rpm, which overstates power.
- Mixing mechanical hp, metric PS and kW. 300 hp is 223.7 kW and 304.2 PS.
- Comparing crank power with wheel power, which is lower after drivetrain losses.
Frequently asked questions
What is the horsepower formula?
hp = torque (lb-ft) x rpm / 5252. An engine making 300 lb-ft at 5000 rpm produces 300 x 5000 / 5252 = 285.6 hp. In SI units, power in watts is torque in N·m times 2 pi times rpm / 60.
Why is the constant 5252?
One horsepower is 33,000 ft-lb per minute, and one revolution is 2 pi radians. 33,000 / (2 pi) = 5252.1, so the constant is rounded. This calculator uses the exact value, so results can differ from the 5252 shortcut in the fourth digit.
How do I convert hp to kW and PS?
One mechanical horsepower is 745.7 W, so 300 hp is 223.7 kW. Metric horsepower (PS, CV, pk) is 735.49875 W, so 300 hp is about 304.2 PS. The page shows all three for any result.
Why do torque and horsepower curves cross at 5252 rpm?
When torque is in lb-ft and power in hp, the two numbers are equal at 5252 rpm, because the formula then reduces to hp = torque. Below that rpm torque is the larger number, above it horsepower is. The figures here are at the crankshaft or wheels depending on how you measured torque.
How do I calculate horsepower from torque in N·m?
Convert to power with P = torque × 2π × rpm / 60, then divide by 745.7 W per hp. For 400 N·m at 6000 rpm that is 251.33 kW, or 337.04 hp (341.71 PS). The same engine is 295.02 lb-ft.
How much horsepower does a 2.0L engine make with 350 N·m?
It depends on the rpm where that torque is made. 350 N·m at 4500 rpm is 164.93 kW or 221.18 hp, and the same torque at 6000 rpm would be about 295 hp. Engine size alone does not fix power.
At what rpm are torque and horsepower equal?
At 5252 rpm when torque is in lb-ft and power in hp. Enter 300 hp and 300 lb-ft in the engine speed mode and you get 5252.11 rpm. Above that rpm the hp number is larger than the lb-ft number.