Horsepower Calculator - Torque & RPM to HP
Calculate horsepower from torque and RPM, in imperial (lb-ft) or metric (N·m) units.
Horsepower
228.5
170.4 kWHow to Calculate Horsepower from Torque and RPM
Horsepower is a measure of the rate at which torque is converted into rotational work. Enter torque and engine speed (RPM), and choose imperial units (pound-feet) or metric units (newton-meters), to get the equivalent horsepower.
Example
An engine producing 300 lb-ft of torque at 4,000 RPM makes HP = (300 × 4,000) ÷ 5,252 ≈ 228.5 horsepower. Note that torque and horsepower curves always cross at exactly 5,252 RPM on an imperial dyno chart, since that's where the two units become numerically equal.
Common Use Cases
- Converting a dyno sheet's torque curve into a horsepower figure at a given RPM.
- Comparing engine outputs specified in different units (lb-ft vs N·m).
- Automotive tuning and engine performance estimates.
FAQs
Where does the constant 5,252 come from?
It comes from converting the definition of mechanical power (torque × angular velocity) into horsepower and RPM units — specifically, 33,000 ft-lb/min per horsepower divided by 2π radians per revolution equals approximately 5,252. It's also the RPM at which the torque (in lb-ft) and horsepower numbers are always identical on a dyno graph.
Should I use imperial or metric units?
Use imperial (pound-feet) if your torque figure comes from a US-spec source, and metric (newton-meters) if it comes from a manufacturer spec sheet using SI units — the calculator applies the matching conversion constant for whichever you select.
Does this account for drivetrain losses?
No — this calculates horsepower directly from the torque and RPM figures you enter (typically crank/engine output). Power actually delivered to the wheels is usually 15-20% lower after accounting for drivetrain losses through the transmission and differential.