Horsepower Calculator
Calculate horsepower from torque and rpm, or estimate it from a quarter-mile time and vehicle weight.
About the Horsepower Calculator
Choose torque and rpm, or quarter-mile time and weight, and enter the values. The calculator gives horsepower and the same power in kilowatts and metric horsepower (PS).
Mechanical horsepower is 550 ft·lbf/s = 745.69987 W. Because hp = torque × rpm ÷ 5,252, torque and horsepower curves cross at 5,252 rpm. The quarter-mile estimate (hp = weight × (5.825 ÷ ET)³) is an empirical drag-racing rule of thumb.
The formula
hp = torque (lb·ft) × rpm ÷ 5252
Worked example
300 lb·ft at 6,000 rpm
- 300 × 6,000 ÷ 5,252 = 342.7 hp
- = 255.6 kW = 347.5 PS
- At 5,252 rpm, horsepower equals torque: 400 lb·ft makes 400 hp
Questions people ask
Brake vs wheel horsepower?
Wheel hp is lower because the drivetrain loses roughly 10–20%.
hp vs PS vs kW?
1 hp = 0.7457 kW; 1 PS = 0.7355 kW.
How do I use N·m?
Multiply N·m by 0.7376 to get lb·ft first.