MasterTool

Horsepower Calculator

Estimate engine horsepower from a drag strip time slip — by trap speed or by elapsed time — using your vehicle's race weight.

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What this tool does

Estimate engine horsepower from a drag strip time slip — by trap speed or by elapsed time — using your vehicle's race weight. ESTIMATES from Hale's empirical relations, fitted to crank horsepower. Drivetrain losses and conditions mean dyno figures will differ.

How to use the Horsepower Calculator

  1. Enter or select primary method.
  2. Enter or select vehicle weight with driver (lb).
  3. Enter or select quarter-mile et (s).
  4. Enter or select trap speed (mph).
  5. Read the calculated result; change any measurement to compare alternatives.

Formula

trap method: HP = weight × (MPH ÷ 234)³; ET method: HP = weight ÷ (ET ÷ 5.825)³ (Hale formulas inverted)
method
Primary method
weight
Vehicle weight with driver (lb)
et
Quarter-mile ET (s)
trap
Trap speed (mph)

ESTIMATES from Hale's empirical relations, fitted to crank horsepower. Drivetrain losses and conditions mean dyno figures will differ.

Worked example

For horsepower calculator, the following measurements illustrate the exact method: Primary method: trap; Vehicle weight with driver (lb): 3500; Quarter-mile ET (s): 13.2; Trap speed (mph): 103.

Inputs

  • Primary methodTrap speed method
  • Vehicle weight with driver (lb)3500
  • Quarter-mile ET (s)13.2
  • Trap speed (mph)103

Result

  • Horsepower from trap speed298.49
  • Horsepower from trap speed298.49
  • Horsepower from ET300.77

Results explained

Horsepower from trap speed
Horsepower from trap speed from the formula above. ESTIMATES from Hale's empirical relations, fitted to crank horsepower. Drivetrain losses and conditions mean dyno figures will differ.
Horsepower from trap speed
Horsepower from trap speed from the formula above. ESTIMATES from Hale's empirical relations, fitted to crank horsepower. Drivetrain losses and conditions mean dyno figures will differ.
Horsepower from ET
Horsepower from ET from the formula above. ESTIMATES from Hale's empirical relations, fitted to crank horsepower. Drivetrain losses and conditions mean dyno figures will differ.

Frequently asked questions

HP ≈ weight × (trap MPH ÷ 234)³ — Hale's formula inverted. A 3,500 lb car trapping 103 mph is making about 300 hp. The trap-speed method is the more reliable of the two because trap speed is barely affected by launch quality.

HP ≈ weight ÷ (ET ÷ 5.825)³. It assumes an efficient launch and run; a car that spins or bogs shows a slow ET and the method under-reads its power.

ET depends on the whole run including the launch; trap speed mostly reflects power in the second half. A gap between the two usually says more about traction and gearing than about the engine.

These strip formulas were fitted against flywheel (crank) ratings of their era. Wheel horsepower on a chassis dyno typically reads 10–20% lower depending on drivetrain.

Race weight: car plus driver, fuel and everything on board during the run — the formulas were derived on that basis.