Quarter Mile Calculator — Drag Racing ET & Trap Speed Estimator
Estimate a vehicle's quarter-mile elapsed time (ET) and trap speed from its weight and engine horsepower using the widely cited Lawlor drag-racing performance formula.
lb
hp
Estimated quarter-mile time from a standing start (Lawlor formula)
- 1
Weight-to-power ratio
3,500 ÷ 350 = 10 - 2
Cube root of ratio
(10)^(1÷3) = 2.154435The cube root captures how drag and rolling resistance scale across the quarter mile. - 3
Elapsed time (ET)
5.825 × 2.154435 = 12.55
How does this calculator work?
Use ET = 5.825 × (W/HP)^(1/3) for elapsed time and 234 × (HP/W)^(1/3) for trap speed in mph. Both scale with the power-to-weight ratio. A 3,500 lb / 350 hp car yields roughly ET ≈ 12.6 s and trap ≈ 109 mph under ideal conditions. Results are estimates — real runs depend on traction, altitude and driver.
Formula
How this is calculated
Drag racing performance is governed primarily by the power-to-weight ratio: how much horsepower each pound of car must accelerate over a quarter mile (1,320 ft). The Lawlor formula (also cited as the Wallace or Hale formula) captures this as ET = 5.825 × (W/HP)^(1/3), where W is vehicle weight in pounds and HP is flywheel horsepower. The cube-root exponent reflects how aerodynamic drag and rolling resistance scale with speed across the run.
The companion trap-speed formula, 234 × (HP/W)^(1/3), estimates the finish-line speed in miles per hour. Together the two formulas are self-consistent: a car that runs a 12-second quarter mile typically traps around 108–115 mph. A heavier car or lower power output shifts ET upward (slower) and trap speed downward on the plotted curve.
These formulas give idealised estimates calibrated to flywheel horsepower under good traction, consistent gearing and standard-atmosphere conditions at sea level. Real-world results are affected by launch grip, tyre preparation, gear ratios, driver technique, altitude, air density and humidity. Different published sources use slightly different constants (some cite 6.290 instead of 5.825, targeting different traction assumptions). Treat the output as a performance benchmark rather than a guaranteed strip result — it is most useful for comparing how changes in weight or power affect potential performance.
Frequently asked questions
For context: a typical stock muscle car runs 13–15 seconds; a high-performance sports car such as a Corvette Z06 around 11 seconds; purpose-built drag cars run into the 6-second range. Most unmodified street cars fall between 13 and 17 seconds.
Yes — enter the total racing weight: the car's curb weight plus driver, fuel load and any ballast. A heavier fuel load at the start penalises ET slightly, while the car lightens as fuel burns during the run.
The Lawlor formula was calibrated to rated (factory) flywheel horsepower. Wheel horsepower (measured on a dynamometer) is typically 15–20% lower due to drivetrain losses. Using wheel HP would underestimate ET. If you only have wheel HP, multiply by roughly 1.15–1.20 to estimate flywheel HP before entering it.
Also known as
TG we-Calculate Editorial Team. (2026). Quarter Mile Calculator — Drag Racing ET & Trap Speed Estimator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/quarter-mile-calculator
TG we-Calculate Editorial Team. "Quarter Mile Calculator — Drag Racing ET & Trap Speed Estimator." TG we-Calculate. 2026. https://we-calculate.com/calculator/quarter-mile-calculator.
TG we-Calculate Editorial Team, "Quarter Mile Calculator — Drag Racing ET & Trap Speed Estimator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/quarter-mile-calculator
@misc{wecalculate_quarter_mile_calculator, title = {Quarter Mile Calculator — Drag Racing ET & Trap Speed Estimator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/quarter-mile-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?