Horsepower Calculator
Horsepower and kilowatts from torque and engine speed, or an estimate from quarter-mile trap speed or time, with power at the wheels and power to weight.
Result
Engine power: 293.2 hp
The quarter-mile methods are rough estimates: aerodynamics, traction and gearing move them a lot.
https://calcgallery.com/vehicle-specs/horsepower-calculator/
Results are arithmetic on the figures you enter. The site stores no vehicle data, fuel prices, mileage rates, depreciation rates or residual values, because they vary by model and place and change over time. Real fuel economy varies with driving, weather and load. Nothing here is a fitment, safety or financial recommendation. Read the full disclaimer
How to use the Horsepower Calculator
- Choose whether to work from torque and engine speed, or to estimate from a quarter-mile trap speed or time.
- Enter torque in lb-ft or Nm with the rpm it was measured at, or the car's weight with the trap speed or time.
- Read the power in hp, kW and PS, and optionally the power at the wheels after the drivetrain loss you enter.
The formulas
power = torque × angular speed = torque × 2π × rpm ÷ 60hp = weight in lb × (trap speed in mph ÷ 234)³ estimatehp = weight in lb ÷ (quarter-mile time ÷ 5.825)³ estimateThe first is physics: power is torque times rotational speed, with torque converted to newton metres and speed to radians per second. The other two are empirical relations fitted to drag-strip results, not physics.
Rated horsepower
Manufacturers rate engines under standard conditions set out in SAE J1349, so figures can be compared fairly. Heat, altitude and humidity all lower the power an engine actually makes on the day.
With your numbers
- P = torque × 2π × rpm ÷ 60 = 218.65 kW = 293.22 hp
Quick reference
The quarter-mile methods are rough estimates: aerodynamics, traction and gearing move them a lot.
| Example | Result |
|---|---|
| 350 lb-ft at 4,400 rpm | Engine power: 293.2 hp |
| 300 lb-ft at 5,252 rpm | Engine power: 300 hp |
| 475 Nm at 4,400 rpm | Engine power: 218.9 kW |
| 3,400 lb at 105 mph trap | Estimated power: 307.2 hp |
| 3,400 lb in 12.8 seconds | Estimated power: 320.4 hp |
| 400 Nm at 6,000 rpm, 15% loss | Engine power: 251.3 kW |
Common questions about the Horsepower Calculator
- Where does 5252 come from?
- One horsepower is 33,000 foot-pounds per minute, and turning a crank through one revolution is 2π radians. So horsepower = torque in lb-ft × rpm × 2π ÷ 33,000 = torque × rpm ÷ 5,252.11. At that engine speed the two numbers are equal, which is why horsepower and torque curves plotted in hp and lb-ft always cross there.
- What is the difference between hp, kW and PS?
- Three units of power. Mechanical horsepower is 745.7 W; the metric horsepower, PS, is 735.5 W, about 1.4% less; a kilowatt is 1,000 W. 100 kW is 134.1 hp or 136.0 PS.
- How accurate are the quarter-mile estimates?
- Roughly. They are rules of thumb from drag racing that assume typical traction, gearing and aerodynamics. A car that loses traction at the start gives a slow time and too low an estimate; a slippery or very light car can give too high a one. Trap speed is usually the steadier of the two.
- What is wheel horsepower?
- Power measured at the wheels on a dynamometer, after losses in the gearbox, driveshafts and differential. The loss varies by car, which is why the page asks for your own figure rather than assuming one.