Drag racing performance estimator
Quarter Mile Calculator
Estimate quarter-mile elapsed time and trap speed from race weight and power, estimate power from a measured run, or convert an eighth-mile pass.
Quarter-mile results
| Scenario | Power | ET | Trap speed |
|---|
Important: these are empirical estimates, not guaranteed passes. A real time slip is the authoritative result.
Quarter-mile formulas
The performance mode uses common empirical drag-racing relationships based on total race weight and effective horsepower:
Effective horsepower means the power available for acceleration in the model. Wheel horsepower is normally the cleaner direct input. When engine horsepower is selected, the calculator applies the user-entered drivetrain-loss assumption before estimating the run.
Checked example
A vehicle weighing 3,420 lb plus a 180 lb driver has a 3,600 lb race weight. At 450 wheel horsepower, the empirical estimate is approximately 11.65 seconds at 117.00 mph. The sensitivity table shows the same model at 10% less and 10% more power.
Estimating horsepower from a time slip
The inverse mode can estimate effective horsepower from ET, trap speed, or both. ET is strongly affected by launch, traction and shifts. Trap speed often reflects power more consistently, but weather, aerodynamics, gearing and measurement still matter. When both are entered, the calculator reports both estimates and their percentage difference instead of pretending they are identical.
Eighth-mile to quarter-mile conversion
The default factors are 1.57 for elapsed time and 1.25 for speed. They are editable because no single factor fits every vehicle. A 7.50-second pass at 95 mph therefore estimates 11.78 seconds and 118.75 mph with the defaults. Treat this as a planning conversion, not a replacement for a quarter-mile time slip.
Limits of a horsepower-and-weight estimate
- It does not model reaction time; ET starts when the vehicle moves, not when the starting light changes.
- It does not calculate 0–60 mph, rollout, density altitude, tire grip, launch strategy, shift duration or aerodynamic drag separately.
- Use total race weight, not brochure curb weight, and do not mix engine horsepower with wheel horsepower when comparing vehicles.
- Track preparation, slope, wind, temperature, altitude, battery state, fuel, driver technique and safety rules can materially change a pass.
- Do not use the estimate to select unsafe speeds, ignore track rules or bypass technical inspection.
Related calculators
Compare performance per unit of mass with the Power-to-Weight Ratio Calculator, calculate road speed and axle relationships with the Gear Ratio Calculator, size fuel delivery with the Fuel Injector Calculator, or compare tire dimensions with the Tire Size Calculator.