Horsepower Calculator
Enter torque and engine speed (RPM) to find the resulting horsepower and kilowatts.
How horsepower is calculated from torque and RPM
The standard formula is HP = (Torque × RPM) / 5252, where torque is in pound-feet and RPM is the engine's rotational speed in revolutions per minute. The constant 5252 comes from converting the units of torque and angular speed into the mechanical definition of horsepower.
This explains why an engine's torque and horsepower curves always cross at exactly 5252 RPM — below that speed torque numerically exceeds horsepower, and above it horsepower exceeds torque, purely as a consequence of this formula rather than any physical phenomenon.
Frequently asked questions
Why does the formula use the specific number 5252?
It's a unit-conversion constant: one horsepower equals 33,000 ft-lb per minute, and converting RPM (revolutions per minute) to radians per minute introduces a factor of 2π, giving 33,000 / (2π) ≈ 5252.
What's the difference between torque and horsepower?
Torque is a measure of rotational force at a given instant, while horsepower is a measure of the rate of doing work — it factors in how fast that torque is being applied (the RPM). An engine can have high torque but low horsepower if it spins slowly, or vice versa.
Is this formula accurate for any engine?
The formula itself is a pure mathematical relationship, always accurate for converting a given torque and RPM pair into horsepower. What varies between engines is how their torque output changes across the RPM range, which a dyno chart shows but a single torque/RPM calculation does not.