drag racing
Quarter-mile ET
Explore empirical quarter-mile elapsed-time and trap-speed estimates from race-ready weight and engine horsepower, with visible model coefficients.
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DRAG RACING CALCULATORTrap Speed
Trap Speed
Calculator
Estimate quarter-mile trap speed from race-ready weight and engine power using an explicitly empirical cube-root model.
Your setup
lb
Include the driver, fuel and equipment.hp
Mechanical horsepower in imperial mode. Use consistent engine-rated power for the empirical model.Your results
CalculatedEmpirical trap speed117mph
Metric speed188.29km/h
Trap speed is an end-of-run measurement, not average speed through the quarter mile.
READ THE ASSUMPTIONS
An empirical model without aero, gearing, wind or power-curve detail. It does not establish engine output.
THE FORMULA
How the calculation works
Follow the formula and keep the input units consistent at every step.
trap MPH = 234 × (HP / W_lb)^(1/3)- Enter race-ready weight and engine power.
- Compute the power-to-weight cube root.
- Multiply by the empirical speed coefficient.
A Worked Example
400 hp / 3,200 lb = 0.125; its cube root is 0.5. Estimated trap speed is 234 × 0.5 = 117 MPH (188.29 KPH).
What Your Result Means
Trap speed is an end-of-run measurement, not average speed through the quarter mile.
Assumptions & Limitations
An empirical model without aero, gearing, wind or power-curve detail. It does not establish engine output.
Common Mistakes
Do not use an eighth-mile speed with this quarter-mile model.
Questions about this calculation
Which values should I enter?
Enter race-ready weight and engine power. Do not use an eighth-mile speed with this quarter-mile model.
How should I interpret the result’s precision?
Displayed results are rounded for readability. Intermediate calculations retain floating-point precision; extra displayed decimals do not improve your input accuracy.
Can I use metric units?
Yes. Select Metric above the calculator to convert your inputs. Results always state their units. Tire-size designations keep their conventional mm and inch units.
What are the main limitations?
An empirical model without aero, gearing, wind or power-curve detail. It does not establish engine output.
Method, sources & relevant guides
Hale coefficient model: ET constant 5.825 and speed constant 234. Lucius documents the formulas and compares them with road-test data. These are empirical relationships, not physical laws or calibrated vehicle predictions.
Jeff Lucius / Stealth 316 — Quarter-mile formulas and original regression analysisMethod documentation updated October 18, 2026. Independent professional review has not been claimed. Read the calculation and review policy.