Horsepower Calculator · Practical guide
How to Calculate Horsepower from Torque and RPM
The HP = torque x RPM / 5252 formula, worked examples in lb-ft and Nm, and instant kW and PS conversions.
At a glance
The Horsepower Formula
To calculate horsepower from torque and RPM, multiply torque in pound-feet by RPM and divide by 5252: HP = (Torque in lb-ft x RPM) / 5252. For example, an engine making 300 lb-ft at 4,000 RPM produces 300 x 4,000 / 5,252 = 228.5 horsepower.
Interactive tool
Horsepower Calculator
Enter your own values, then compare the result with the examples below.
Results
Worked Example
Take a V8 rated at 400 lb-ft of torque at 4,500 RPM: 400 x 4,500 / 5,252 = 342.9 hp. The same engine at a 6,000 RPM point where torque is 380 lb-ft makes 380 x 6,000 / 5,252 = 434.1 hp — peak horsepower usually sits higher in the rev range than peak torque.
Using Newton-Meters
If your spec sheet lists torque in newton-meters, convert first: divide Nm by 1.3558 to get lb-ft. A European sedan rated at 400 Nm makes 400 / 1.3558 = 295.0 lb-ft, so at 3,000 RPM it produces 295.0 x 3,000 / 5,252 = 168.5 hp. The calculator above accepts Nm directly and does this conversion for you.
Converting to kW and PS
Once you have horsepower, two quick multipliers cover the other common units: kilowatts = hp x 0.7457 and metric horsepower (PS) = hp x 1.0139. That 342.9 hp V8 equals 255.7 kW or 347.7 PS. Enter torque and RPM above to get all three units at once.
Frequently Asked Questions
Where does the number 5252 come from?
One horsepower is defined as 33,000 foot-pounds of work per minute. Since one revolution sweeps 2pi feet at a one-foot radius, the combined constant is 33,000 / 2pi, which is about 5252.
Does gearing change horsepower?
No. Gearing multiplies torque at the wheels, but RPM drops by the same ratio, so horsepower stays the same apart from drivetrain losses of roughly 10-20%.
Is this crank or wheel horsepower?
The formula gives engine (crank) horsepower from measured torque. Wheel horsepower from a chassis dyno reads lower because of drivetrain friction.
Does the formula work for electric motors?
Yes. It applies to any rotating machine where torque and RPM are known, including electric motors and industrial equipment.