The Engine Horsepower Calculator estimates a vehicle's horsepower from its weight and quarter-mile time or trap speed.
Estimated engine horsepower: 123.5 hp
| Horsepower (ET method) | 123.5 |
| Kilowatts | 92.1 |
Estimated engine horsepower: 133.8 hp
| Horsepower (trap speed method) | 133.8 |
| Kilowatts | 99.8 |
Quarter-mile results reveal power: a heavier car needs more horsepower to cover 1/4 mile in the same time. Two classic formulas estimate wheel horsepower from weight and either elapsed time or trap speed.
ET method: hp = weight (lb) × (5.825 ÷ ET)³. Trap speed method: hp = weight × (speed in mph ÷ 234)³.
Worked example (defaults): 5,000 lb and a 20-second ET give 5,000 × (5.825 ÷ 20)³ ≈ 123.5 hp. A 70 mph trap speed gives 5,000 × (70 ÷ 234)³ ≈ 133.9 hp.
Trap speed is less affected by launch technique and traction, so it is usually more reliable. Results approximate wheel horsepower; engine (crank) horsepower is typically 10–20% higher because of drivetrain losses.
Should weight include the driver? Yes.
Why do my results differ from a dyno? Weather, altitude, gearing and traction affect times.
Can I use 1/8 mile times? Not with these formulas.