Engine Horsepower Calculator
Estimate engine horsepower from quarter-mile elapsed time (ET) and trap speed, using Roger Huntington's empirical formula.
How to use the Engine Horsepower Calculator
- Enter your inputs into the Engine Horsepower Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The quarter-mile HP formula
HP = Weight × (MPH / 234)³ · · · or HP = Weight / (ET / 5.825)³
Weight is curb weight + driver in pounds; MPH is trap speed at the quarter-mile finish; ET is elapsed time. Roger Huntington's formulas approximate HP at the wheels from real-world drag strip performance.
Worked example
A 3,200 lb car running 12.5 seconds at 115 MPH: HP from MPH = 3,200 × (115/234)³ ≈ 380 hp. HP from ET = 3,200 / (12.5/5.825)³ ≈ 376 hp. Wheel HP, not crank HP.
Frequently asked questions
Are these estimates accurate?
Within ±5–10% for typical drag racing scenarios. Most accurate for vehicles with strong launches and minimal aerodynamic complications. Less accurate for very high-HP cars where aero matters more.
Does this include drivetrain losses?
Yes — it produces HP at the wheels. To estimate crank HP, divide by 0.85 (manual) or 0.80 (automatic) approximately.
Why do trap speed and ET give different HP?
They measure different things. Trap speed reflects sustained power; ET reflects power + launch effectiveness. Use trap speed as the primary HP indicator; ET varies more with launch technique.