Estimate your vehicle's engine horsepower from its weight and either a quarter-mile trap speed or elapsed time, using the standard drag racing horsepower formulas.
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The trap speed method uses the formula: Horsepower = Weight × (Trap Speed ÷ 234)³, based on the vehicle's weight and its speed at the end of a quarter-mile run. The elapsed time method instead uses: Horsepower = Weight ÷ (Elapsed Time ÷ 5.825)³, based on how long the quarter-mile took. Both are widely used drag-racing estimation formulas, fill in whichever measurement you have.
These formulas give a rough estimate of flywheel horsepower and don't account for aerodynamic drag, tire grip, driver skill, altitude or weather conditions, all of which affect real quarter-mile performance. Use this as a general reference, not a dyno-certified figure.
A 3,400 lb car running a quarter-mile at a 100 mph trap speed: horsepower = 3,400 × (100 ÷ 234)³ ≈ 265.36 hp. If instead you only recorded a 13-second elapsed time for the same car, the other formula gives horsepower = 3,400 ÷ (13 ÷ 5.825)³ ≈ 305.87 hp, a meaningfully different estimate, since elapsed time is more sensitive to launch technique and traction than trap speed is, trap speed is generally considered the more reliable of the two when you have both.
Using the vehicle's curb weight instead of its actual weight as raced, forgetting to include the driver, a full fuel tank, or any ballast understates the true weight and throws off the horsepower estimate in either formula.
Filling in both trap speed and elapsed time and expecting them to be averaged, the calculator uses trap speed if it's provided, only falling back to elapsed time if trap speed is left blank, it doesn't combine the two.
Treating the result as a dyno-certified figure, these are widely used drag-racing estimation formulas based purely on weight and quarter-mile performance, they don't account for aerodynamic drag, tire grip, altitude or weather, real dyno-measured horsepower can differ meaningfully from this estimate.
Trap speed is generally considered the more reliable indicator of horsepower, since elapsed time is more sensitive to launch technique and traction. If you have both, the trap speed method is usually preferred.
Use the vehicle's total weight as raced, including the driver and any fuel or ballast, not just the vehicle's curb weight alone.
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