How the horsepower calculator works
Horsepower measures how fast work is done; torque measures twisting force. Power is torque multiplied by rotational speed.
kW = HP × 0.7457 · N·m = lb-ft × 1.3558
The constant 5,252 comes from James Watt's definition of one horsepower as 33,000 ft·lb per minute, divided by 2π radians per revolution. Because of it, any engine's torque and horsepower curves cross at 5,252 RPM when plotted in lb-ft and hp. Engine figures are usually measured at the crankshaft; wheel horsepower is 10% to 20% lower due to drivetrain losses.
Worked example
An engine making 400 lb-ft at 4,000 RPM produces 400 × 4,000 ÷ 5,252 = 304.6 hp, or 227.2 kW. In metric terms that torque is 542.3 N·m. At 5,252 RPM, 300 lb-ft would equal exactly 300 hp.
Frequently asked questions
How do I convert torque to horsepower?
Multiply lb-ft by RPM and divide by 5,252.
Why do torque and horsepower cross at 5,252 RPM?
Because HP = torque × RPM ÷ 5,252, so at 5,252 RPM the two numbers are equal.
What is the difference between hp and kW?
Both measure power; 1 hp is 745.7 W, so 1 kW is about 1.341 hp.
Is more torque or more horsepower better?
Torque gives low-speed pulling force; horsepower determines top-end performance. Gearing turns one into the other.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.