Performance / Estimate
Quarter Mile Calculator: ET, Trap Speed and Horsepower
Use the Hale-style empirical power-to-weight formulas for rough quarter-mile time and trap speed estimates, or estimate equivalent horsepower from ET or trap speed.
Quarter Mile Calculator: ET, Trap Speed and Horsepower: Applies ET = 5.825 × (lb/hp)^(1/3) and trap mph = 234 × (hp/lb)^(1/3), or their algebraic inverses. These rough empirical estimates do not account separately for traction, aerodynamics, shifting or power measurement. They are not a dyno measurement. Runs 100% locally in your browser with zero server file uploads.
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ET = 5.825 × (lb/hp)^(1/3); trap mph = 234 × (hp/lb)^(1/3). Reverse: hp = lb × (5.825/ET)³, or hp = lb × (mph/234)³.
These Hale-style empirical formulas give rough estimates. Traction, gearing, aerodynamic drag, shifting, weather and power measurement can change the result substantially. Reverse results are formula-equivalent horsepower, not a dyno measurement. No wheel-to-crank power correction is applied.
Elapsed time excludes the driver's start-line reaction time. Use total running weight, including driver and fuel. The two estimates share the same simplified power-to-weight model.
Empirical model
The Hale-style coefficient pair used here is ET = 5.825 × (weight in lb / mechanical hp)^(1/3), and trap mph = 234 × (hp / lb)^(1/3). These are fitted estimates, not physical laws. Automotive textbook background: John Lawlor and Bill Hancock, Auto Math Handbook, HP Books, revised edition, 2011, chapter Quarter-mile E.T. and MPH. Bibliographic record: https://libcatalog.neit.edu/cgi-bin/koha/opac-ISBDdetail.pl?biblionumber=71599
Reverse calculation and limits
Rearrangement gives hp = lb × (5.825/ET)³ or hp = lb × (trap mph/234)³. For 3200 lb and 400 hp, the cube-root weight/power ratio is 2: ET is 11.65 s and trap speed 117 mph. No drivetrain-loss correction or 0–60 mph estimate is included.
How to use it
- Choose weight and horsepower, weight and ET, or weight and trap speed.
- Enter total running weight including driver and fuel, then the known value.
- Read ET, trap speed and formula-equivalent power, keeping the model's limits in mind.
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Frequently asked questions
Which weight belongs in the calculation?
Use total running weight in pounds, including the driver, fuel and equipment carried during the run.
Is the reverse result wheel or crank horsepower?
It is formula-equivalent mechanical horsepower. This calculator does not apply a drivetrain-loss correction and cannot establish a wheel-to-crank relationship from ET or trap speed alone.
Why might ET and trap speed imply different horsepower?
The simplified formulas share a power-to-weight model, but a real launch, traction, gear changes, power curve, weather and aerodynamic drag can affect measured ET and trap speed differently. ET excludes start-line reaction time.
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