1/4 Mile HP Calculator

Estimate horsepower from your 1/4 mile time and race weight, or your quarter-mile ET from horsepower, with an estimated trap speed in mph and km/h.

Calculator Functions

The calculator links horsepower, race weight and quarter-mile elapsed time, so any two give the third. Every function also estimates trap speed. Select a function to open it in the calculator.

Function	Use it when	You enter
Horsepower	You have a time slip and want to estimate power	Total race weight and elapsed time
Quarter-mile elapsed time	You want to predict a run from power	Total race weight and horsepower
Total race weight	You want the weight that fits a power and time	Horsepower and elapsed time

Race weight covers the vehicle, driver, fuel and anything carried on the run, in lb or kg. Use the elapsed time on the slip, not counting reaction time.

1/4 Mile HP Formulas

Quarter-mile elapsed time uses this directly. A 3,200 lb car with 400 hp comes out at 5.825 × (8)^1/3 = 11.65 seconds.

Horsepower and Total race weight

Both rearrange the same formula. A 3,200 lb car running 13.00 seconds comes out at about 288 hp.

Estimated trap speed

This is a separate empirical formula with the same cube-root form [2], shown in mph and km/h, with 1 mile = 1.609344 km [1]. The 3,200 lb, 400 hp car gives 117 mph.

Limits of This Estimate

• An empirical performance estimate, not a dynamometer measurement. Traction, shifts, gearing, weather and track conditions all change real runs.
• The 5.825 and 234 coefficients are rules of thumb, not values derived from physics. These estimates are based on the best available data and estimations.
• The estimate does not separate wheel from crankshaft horsepower or account for drivetrain loss, so power entered or solved on one basis stays on that basis.

Sources