semku1/4 mile calculator
Estimate drag-strip elapsed time and quarter-mile trap speed from weight and horsepower, or estimate horsepower from a quarter-mile time slip.
Include the driver, fuel, passengers and everything carried in the vehicle.
Enter wheel horsepower. No drivetrain-loss conversion is applied.
Enter elapsed time, trap speed, or both from a quarter-mile time slip. Do not add reaction time or enter an eighth-mile result.
These are input limits, not a validated accuracy range.
Model estimates
60 ft ET (s) 1.78
1/8 mile ET (s) 7.88
1/4 mile ET (s) 11.65
1/4 mile trap speed (mph) 123.0
These are separate estimates. A difference between them is not a measured drivetrain loss.
These empirical estimates do not simulate your vehicle. Traction, gearing, shifting and conditions can change the result. They are not dyno measurements or guaranteed track results.
Estimate formula (q = (weight ÷ wheel hp)^(1/3)): 1/4 mile ET = 5.825 × q; trap speed = 246 ÷ q; 60 ft ET = 0.138 × ET + 0.17; 1/8 mile ET = 0.695 × ET − 0.22.
A quarter mile is 1,320 ft, or 402.336 m.
Model, assumptions and sources
Forward estimate: q = (W ÷ P)^(1/3), where W is total race weight in lb and P is wheel horsepower. 1/4 mile ET = 5.825 × q seconds; 1/4 mile trap speed = 246 ÷ q mph; 60 ft ET = 0.138 × ET + 0.17 seconds; 1/8 mile ET = 0.695 × ET − 0.22 seconds.
Horsepower estimates invert the same formulas: P = W × (5.825 ÷ ET)^3 and P = W × (trap speed ÷ 246)^3. They are algebraic inverses of this model, not independent measurements.
Applicability: a standing-start, level, straight quarter-mile comparison estimate. Traction, aerodynamics, weather, gearing, shifting and power curve are not modeled separately. No accuracy range is claimed.
Shorter-distance times are derived from the unrounded quarter-mile ET. ET values are shown to 2 decimal places, speed and horsepower to 1, with an exact halfway value rounded up.
Sources
Rob Robinette — 1/4 Mile ET Calculator
Published implementation of the empirical formulas used here. It does not publish calibration data or an accuracy range.
Geoffrey T. Fox — On the Physics of Drag Racing (1973)
Constant-power physics background for the cube-root relationship. It is not the source of the empirical coefficients.
NIST — Revised Unit Conversion Factors
One mile is 5,280 ft or 1,609.344 m, so a quarter mile is 1,320 ft or 402.336 m.
Frequently asked questions
- Should I enter wheel or crank horsepower?
- Enter wheel horsepower in mechanical hp, not metric PS. The calculator applies no drivetrain-loss conversion.
- Why do the ET and trap-speed horsepower estimates differ?
- They invert different empirical relationships. Entered timing and speed data need not agree with both. The calculator keeps the results separate.
- Can I use a 400 m or eighth-mile time slip?
- No. Reverse calculations require a full quarter-mile result. The displayed shorter-distance times are estimates, not conversions of a measured time slip.
- Does trap speed mean average speed for the whole run?
- No. Use the quarter-mile trap-speed reading from the time slip. Dividing the full distance by elapsed time produces a different quantity.
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Calculations run in your browser without sending your calculation inputs or results to the server. See “Privacy on this page” for information about access data.