Math
Horsepower Calculator
Solve HP = (torque x RPM) / 5252, or estimate power from 1/4 mile ET, trap speed, or kilowatts. Outputs mechanical HP, metric HP (PS), and kW.
Horsepower Calculator
HP = (torque x RPM) / 5252. The classic dyno identity.
Engine torque in pound-feet. Must be greater than zero.
Engine speed in revolutions per minute.
Horsepower
400 HP
Mechanical HP
400 HP
Metric HP (PS)
405.5479 PS
Kilowatts
298.28 kW
Torque
400 lb-ft
For reference
- Family sedan: 120-200 HP
- Sports car: 300-500 HP
- Supercar: 500-700 HP
- Hypercar: 700-1200 HP
Frequently Asked Questions about the Horsepower Calculator
What is the horsepower formula from torque and RPM?
HP = (torque x RPM) / 5252, where torque is in pound-feet and RPM is engine speed. The 5252 constant comes from the definition 1 HP = 33,000 ft-lb per minute combined with the 2 pi factor that converts revolutions to ft-lb of work.
What is the difference between mechanical HP and metric HP (PS)?
Mechanical HP is the US and UK automotive standard: 1 HP = 745.6999 W. Metric HP, also called PS or CV, is the German and EU standard: 1 PS = 735.49875 W. A car rated at 100 mechanical HP is about 101.4 PS.
How do you estimate horsepower from a 1/4 mile elapsed time?
The Roush/Hale formula gives HP = weight x (5.825 / ET)^3, where weight is in pounds and ET is the quarter-mile elapsed time in seconds. For a 3,000 lb car with a 12-second ET, that works out to about 343 HP at the engine.
How do you estimate horsepower from quarter-mile trap speed?
Use Hale trap-speed formula: HP = weight x (mph / 234)^3. Trap speed depends more on raw power and less on launch, traction, and shift technique, so it is often more reliable than the ET formula.
How do I convert kilowatts to horsepower?
Multiply kW by 1.34102 to get mechanical HP, or by 1.35962 to get metric HP. So 100 kW is about 134.1 mechanical HP or 136.0 PS. European brochures usually quote kW first, then PS in parentheses.