Horsepower Calculator (from Torque and RPM)
Convert torque and rpm into horsepower and kilowatts.
Torque and horsepower
Horsepower is the rate of doing work, and torque is the twisting force. They are linked by engine speed: horsepower = torque × rpm ÷ 5252 when torque is in pound-feet. That is why an engine’s torque and horsepower lines always cross at 5,252 rpm.
Example
With the starting values shown (Torque 300; Torque unit lb-ft; Engine speed 5000 rpm), Horsepower comes out as 285.6. Other results include kilowatts: 213; metric horsepower: 289.6.
These figures are at a single rpm. An engine’s power changes across its rev range, so use the torque reading at the rpm you care about. Crank power and wheel power also differ because of drivetrain losses.
Frequently asked questions
Why 5252?
It comes from the unit conversion 33,000 ÷ (2π), which links lb-ft, rpm and horsepower.
What is the difference between hp and PS?
A metric horsepower (PS) is about 1.4% smaller than a mechanical horsepower.
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