How to use this calculator
- Enter or choose calculate from.
- The horsepower (mechanical) updates as you type. Use Copy result or Share to keep it.
Method
P (W) = Torque (N·m) × RPM × 2π ÷ 60; P = Force × Distance ÷ Time; hp = W ÷ 745.69987; PS = W ÷ 735.49875; in US units hp = lb·ft × RPM ÷ 5,252
- 1 hp
- 550 ft·lbf/s = 745.69987 W
- 1 PS
- 75 kgf·m/s = 735.49875 W
- 1 lb·ft
- 1.3558179 N·m
Worked example
- Angular speed: 6,000 rpm × 2π ÷ 60 = 628.32 rad/s.
- Power: 400 N·m × 628.32 = 251,327 W = 251.3 kW.
- In horsepower: 251,327 ÷ 745.7 = 337.0 hp, or ÷ 735.5 = 341.7 PS.
400 N·m at 6,000 rpm is about 251 kW, 337 hp or 342 PS.
What the result means
Peak power usually occurs at higher rpm than peak torque. Quoted engine figures are measured at the crankshaft; power at the wheels is lower because of drivetrain losses.
Assumptions and limits
- Mechanical (imperial) horsepower of 745.7 W unless PS is stated.
- Electrical horsepower (746 W) and boiler horsepower are different units and are not shown.
Questions
Why do torque and horsepower curves cross at 5,252 rpm?
In US units hp = lb·ft × rpm ÷ 5,252, because 33,000 ft·lbf per minute ÷ 2π ≈ 5,252. At that speed the two numbers are equal.
Is PS the same as bhp?
No. PS (metric horsepower) is 735.5 W, about 1.4% less than a mechanical horsepower. “bhp” means horsepower measured at the engine’s output shaft.