Horsepower 1/4 Mile Calculator
Estimate quarter mile elapsed time and trap speed from vehicle weight and power. Choose wheel or crank power, set drivetrain loss, add an altitude power-loss adjustment, select traction quality, and optionally apply 1 ft rollout. Real results depend on gearing, aero, shift time, tire, surface, and weather.
Inputs
Reverse solver
Baseline equations: ET ≈ kET × (Weight/WHP)^(1/3), Trap ≈ kMPH × (WHP/Weight)^(1/3). Standard constants use kET = 5.825 and kMPH = 234. Alternative constants reflect stricter or different assumptions. Rollout reduces indicated ET by a small fixed amount.
Results
Effective wheel horsepower used
ET estimate
Trap speed
Power to weight
Power required for target ET
Power required for target trap
Estimates assume steady power delivery and clean shifts. Aerodynamics, gearing, torque curve, tire compound, and weather can move real results up or down.
Frequently Asked Questions
Which power value should I enter, wheel horsepower or crank horsepower?
Use wheel horsepower (WHP) if you have it, since it already removes drivetrain losses. If you only know crank horsepower, select Crank HP (BHP) and set a drivetrain loss, for example 15 percent for typical rear wheel drive, 12 percent for front wheel drive, or 20 percent for all wheel drive.
How accurate are the ET and trap speed formulas?
They are rule of thumb equations based on power to weight, so they are good for ballpark planning. Real cars can be quicker or slower based on gearing, torque curve, shift time, traction, aerodynamics, weather, and track prep.
What do the two formula sets mean, Standard and Alternative?
Drag calculators commonly use constants around 5.825 for ET and 234 for mph. Some references use 6.269 and 225 instead. The alternative set yields slightly slower ET and lower trap speed for the same power. Pick the set that best matches your local results.
What does the traction quality option do?
It adjusts the ET result. Poor traction increases ET a little, for example factor 1.04. Very good launch reduces ET slightly, for example factor 0.97. The trap speed uses power and weight and is not modified by the traction factor.
What is rollout and why does it change ET?
Many timing systems use a 1 foot rollout at the start beam. This reduces the recorded ET by a small amount compared to a strict zero foot start. The toggle subtracts about 0.30 seconds from ET as a simple approximation.
How should I use altitude or density altitude in this calculator?
Altitude and high DA reduce engine power, especially for naturally aspirated setups. If you race at elevation, enter a power loss percentage to reduce the effective wheel horsepower. A small loss makes a noticeable difference in both ET and trap speed.