Horsepower Calculator
Estimate engine horsepower from vehicle weight and quarter-mile trap speed using Huntington's formula — plus rough wheel-to-crank conversion.
What is Horsepower Calculator?
This horsepower calculator uses the classic Roger Huntington trap-speed formula to estimate engine horsepower from your best quarter-mile trap speed and race weight. Accurate within a few percent for traction-limited and power-limited passes alike.
Drag strips worldwide use this as the quick-and-dirty way to estimate power without a dyno.
Formula
HP = weight × (trap ÷ 234)³
Where weight is in pounds including the driver and trap speed is in mph at the quarter-mile mark.
Wheel horsepower (what a chassis dyno reads) subtracts drivetrain loss:
- FWD: ~12%
- RWD: ~15%
- AWD: ~20%
Worked example
A 3,500 lb car with driver runs a 110 mph trap:
- HP = 3,500 × (110 / 234)³
- HP = 3,500 × 0.4701³ ≈ 3,500 × 0.1039
- ≈ 364 flywheel HP
- Wheel HP (RWD) ≈ 364 × 0.85 ≈ 309 whp
How to use this calculator
- Use your race weight (vehicle + driver + fuel + any ballast) in pounds.
- Use mph at the quarter-mile, not 60-foot or 330-foot speeds. 1/8-mile trap is not a substitute.
- Pick drivetrain to get a rough wheel HP figure — actual dyno numbers vary by a few percent from this estimate.
Frequently asked questions
How accurate is the Huntington formula?
Usually within 3–5% of dyno horsepower for traction-limited passes on a well-prepped strip. Sloppy launches, unusual aerodynamics (wings, diffusers), or slippage in the converter can introduce more error.
Why trap speed instead of ET?
Elapsed time (ET) is strongly affected by launch quality and 60-foot time. Trap speed at the end of the quarter is a much more reliable integrator of total power produced over the run.
Does altitude affect the number?
Yes — air density changes engine output. A pass at 5,000 ft elevation is typically about 15% lower in HP than at sea level. Use the trap speed you actually see at the track; it already reflects the real power on that day.
How does HP/lb translate to real-world acceleration?
Under 50 hp per 1,000 lb is economy-car territory. 75–100 is hot-hatch / sport sedan. 150+ is sports car. 200+ is supercar. Weight matters just as much as horsepower — lighter cars feel faster per HP.