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Engine Horsepower Calculator

Estimate engine power from quarter-mile trap speed or ET.

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Formula estimates

FormulaWheel hpFlywheel hp

What other trap speeds would imply

Trap speedWheel hpFlywheel hpPower to weight

Estimated flywheel horsepower

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Details

Wheel horsepower—
Drivetrain loss—
Total race weight—
Formula spread—

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Power to weight, in hp per ton

Trap speed is the more reliable input, because elapsed time depends heavily on traction and launch quality while terminal speed reflects the power actually available. These formulas estimate power at the wheels; the flywheel figure adds a typical drivetrain loss back on. Expect about 10 percent error.

Quick Tool Overview

The Engine Horsepower Calculator estimates power from how a car actually performs — quarter-mile trap speed or elapsed time together with vehicle weight — using the Fox, Hale and Huntington formulas, then adds drivetrain loss back for a flywheel figure.

What it does
Estimates engine power from quarter-mile performance
You give it
Trap speed or elapsed time, and vehicle weight
You get back
Wheel and flywheel horsepower from several formulas
Best for
Drag racing, tuning checks and sanity-testing claims
Calculators Free, unlimited use No sign-up Runs in your browser

About the Engine Horsepower Calculator

Estimate an engine's power from how the car actually performs, rather than from torque figures. Enter a quarter-mile trap speed or elapsed time along with the vehicle weight, and several published formulas are calculated together.

Trap speed is the more reliable of the two inputs, because elapsed time is heavily influenced by how well the car launched, while terminal speed reflects the power that was actually available through the run. Both approaches estimate power at the wheels, so a drivetrain loss has to be added back to reach a flywheel figure — typically 15 percent for a manual rear-wheel-drive car and more for an automatic or all-wheel drive.

Key features of the Engine Horsepower Calculator

Three published formulas

Fox, Hale and Huntington calculated together, with an average and the spread between them.

Trap speed preferred

The page explains why terminal speed is more reliable than ET, which depends heavily on the launch.

Drivetrain loss added back

Manual, automatic and all-wheel drive each carry a different loss, converting wheel power to flywheel.

Weight includes the driver

Because that is what actually accelerated, and leaving it out inflates the estimate.

Accuracy stated

Within about 10 percent — an indication rather than a dyno reading.

How to use the Engine Horsepower Calculator

  1. 1

    Choose an input

    Quarter-mile trap speed, or elapsed time. Trap speed is the more reliable.

  2. 2

    Enter the vehicle weight

    Including the driver and fuel, since that is what actually accelerated.

  3. 3

    Compare the formulas

    Fox, Hale and Huntington are calculated together with an average.

  4. 4

    Add drivetrain loss

    Choose your layout to convert the wheel figure into a flywheel estimate.

Frequently asked questions

The Fox formula is horsepower = weight × (trap speed ÷ 234)³. It estimates power at the wheels from the terminal speed of a quarter-mile run.

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