- Home
- Auto & Travel
- Horsepower Calculator
Horsepower Calculator
Calculate horsepower from torque and engine speed, or estimate it from a quarter-mile run. Choose the method, then enter torque and RPM, or the vehicle weight with either its elapsed time or its trap speed.
- Kilowatts
- 273.32 kW
- Metric horsepower
- 371.61 PS
- Weight per horsepower
- —
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Choose torque and RPM, quarter-mile elapsed time, or trap speed.
- For torque, enter the torque figure and the RPM it was measured at.
- For quarter-mile methods, enter the vehicle weight including the driver.
- Enter the elapsed time in seconds or the trap speed and read the horsepower.
Worked examples
350 lb·ft of torque at 5,500 RPM
- Horsepower
- 366.53 hp
- Kilowatts
- 273.32 kW
A 3,500 lb car running the quarter mile in 13.5 seconds
- Horsepower
- 281.16 hp
- Weight per horsepower
- 12.45 lb/hp
A 3,500 lb car crossing the line at 105 mph
- Horsepower
- 316.22 hp
- Weight per horsepower
- 11.07 lb/hp
Where 5,252 comes from
One horsepower is 33,000 foot-pounds of work per minute. Torque times RPM times 2π gives foot-pounds per minute, and 33,000 ÷ 2π is 5,252. A consequence is that an engine’s torque and horsepower curves, plotted in lb·ft and hp, always cross at 5,252 RPM.
In metric units, power in kilowatts = torque in N·m × RPM ÷ 9,549. Metric horsepower (PS) is slightly smaller than mechanical horsepower: 1 hp = 1.014 PS.
About the quarter-mile estimates
The elapsed-time and trap-speed formulas are long-standing empirical rules of thumb from drag racing, not physical laws. They assume good traction and a well-matched setup. Elapsed time depends heavily on launch and traction, so the trap-speed method is generally the better indicator of power.
Treat either result as a rough estimate and expect the two methods to disagree for the same run. Weight must include the driver and fuel.
Questions people ask
How do I convert torque to horsepower?
Multiply torque in lb·ft by RPM and divide by 5,252. 350 lb·ft at 5,500 RPM is 366.5 hp.
How much horsepower does it take to run a 13.5 second quarter mile?
For a 3,500 lb car, about 281 hp by the elapsed-time formula. A lighter car needs proportionally less.
What is 300 hp in kW?
223.7 kW. Multiply horsepower by 0.7457.