Drag Racing ET and Trap Speed Calculator

Estimate quarter-mile elapsed time and terminal speed from peak engine horsepower and total race-ready vehicle weight. The calculator converts metric inputs, shows power-to-weight context, and keeps every value in your browser.

Track estimate—not a guaranteed time slip These are independent first-order correlations. Actual ET and trap speed depend on traction, power delivery, gearing, shifts, aerodynamics, weather, track preparation, and driver technique. Test only at a sanctioned facility under its rules.

Horsepower and race weight

Use peak engine/flywheel power. Do not mix wheel horsepower with the formula's engine-power basis.

Include the driver, fuel, fluids, safety equipment, and anything carried during the pass.

Privacy: horsepower and weight values are calculated locally. They are not uploaded, stored, or included in analytics events.

Quarter-mile estimate

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Quarter-mile ET and trap-speed formulas

This calculator uses Patrick Hale's simple empirical relationships. It converts input power to mechanical horsepower and weight to pounds before calculating:

ET (seconds) = 5.825 × ∛(weight lb ÷ horsepower)
trap speed (mph) = 234 × ∛(horsepower ÷ weight lb)

ET is the elapsed time over 1,320 ft (402.336 m). Trap speed is the terminal speed reported near the finish—not the average speed over the run. The two equations are separate power/weight correlations, so their outputs should not be treated as a guaranteed matched pair.

The formulas use peak engine power at the clutch/flywheel. If the only available figure is wheel horsepower, first obtain a defensible engine-power estimate or compare against real passes using the same wheel-power basis; do not assume a universal drivetrain-loss percentage.

How to make a useful estimate

  1. Use the correct power basis. Enter mechanical peak engine/flywheel horsepower, or choose kW or PS when the published engine rating uses that unit.
  2. Weigh the race-ready combination. Include the driver, fuel, fluids, safety gear, ballast, and carried equipment—not just curb weight.
  3. Calculate both references. ET is more affected by the launch and early run; trap speed often tracks power-to-weight more consistently.
  4. Calibrate with timing slips. Compare the estimate with repeat passes at the same facility and conditions before using it as a baseline.

Why actual ET and trap speed differ

Horsepower and weight are major influences, but they do not describe the complete run. Two vehicles with the same ratio can produce different timing slips.

  • Launch and traction: tire, surface, suspension, torque management, wheelspin, and wheelstand behavior strongly affect ET.
  • Power delivery: the complete torque curve, boost response, battery state, thermal limits, and engine operating range matter more than one peak number.
  • Driveline: gearing, converter or clutch behavior, rotating inertia, shift points, shift time, and drivetrain loss change acceleration.
  • Resistance and weather: aerodynamic drag, frontal area, rolling resistance, wind, temperature, pressure, humidity, and density altitude influence performance.

A slow launch can produce a worse ET while the car still records a comparatively strong trap speed. Conversely, a well-optimized launch can improve ET without an equivalent increase in terminal speed.

Drag racing calculator FAQs

What formulas does this calculator use?

It uses Patrick Hale's first-order quarter-mile equations: ET = 5.825 × ∛(weight ÷ hp), and trap mph = 234 × ∛(hp ÷ weight). The required base units are pounds and mechanical horsepower.

Should race weight include the driver?

Yes. Use total race-ready weight including the driver, fuel, fluids, safety equipment, ballast, and anything else carried during the pass.

Should I enter crank horsepower or wheel horsepower?

The published relationship is based on peak engine or flywheel power, so enter a mechanical-horsepower figure on that basis. Wheel horsepower is measured after drivetrain losses and is not directly interchangeable.

Why might my actual ET be slower?

The simple equation cannot model launch traction, the shape of the power curve, gearing, shifts, converter or clutch behavior, aerodynamics, rolling resistance, weather, track surface, or driver technique. Hale's ET equation can be optimistic for typical street cars.

Are the ET and trap speed from one matched pass?

No. They are independent correlations calculated from the same horsepower and weight. A real vehicle can pair a slower ET with a similar trap speed because the launch and early run affect ET more strongly.

Does reaction time change ET?

On a standard drag-strip timing slip, ET starts when the vehicle leaves the starting line. Reaction time is measured separately, so it is not added to the ET shown here.

Can I use this for an eighth-mile race?

No. The results specifically estimate a quarter mile: 1,320 feet or 402.336 metres. The page does not derive eighth-mile splits.

Are my inputs tracked?

No. The calculation runs locally in your browser and does not upload, store, or attach horsepower or weight to analytics events.

Limits and motorsport safety disclaimer

  • The equations are empirical estimates, not a simulation, engineering certification, vehicle setup recommendation, or performance guarantee.
  • They do not correct power for weather or density altitude and do not model tire grip, drivetrain loss, power curves, gearing, aerodynamics, or track conditions.
  • Published validation indicates the simple ET relationship has more scatter than the trap-speed relationship and can overstate the performance of typical street cars.

Safety disclaimer: Never test acceleration or top speed on public roads. Use a sanctioned motorsport facility, comply with its technical and safety rules, wear required protective equipment, and have vehicle changes inspected by qualified professionals.

Methodology and sources

Last reviewed: August 2, 2026. Constants and limitations were checked against formula history, comparative road-test analysis, and motorsport calculator documentation:

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