Quarter Mile Calculator

This calculator estimates a quarter mile elapsed time and trap speed from race weight and horsepower, using the three cube root formulas drag racers have relied on for decades: Hale, Fox and Huntington. Enter the weight of the car as it runs and its power at the flywheel or at the wheels, and each formula is shown with its own numbers plus the average of the three. The second mode runs the arithmetic the other way, turning a trap speed off a timeslip back into horsepower. Every figure here is an estimate from weight and power alone, so it knows nothing about traction, gearing, the launch or the air, and a car that spins its tyres will be slower than any of them.

Calculator Type

Weight In

Pounds Kilograms

A pound is 0.45359237 kg exactly, so 3,500 lb is 1,587.57 kg.

Power In

Horsepower (hp, bhp) Kilowatts (kW) Metric horsepower (PS, ch, CV)

One kilowatt is 1.341022 hp and one metric horsepower is 0.986320 hp, so 400 hp is 298.28 kW or 405.55 PS. The formulas were fitted to horsepower, so whatever you pick is converted to it first.

Speed In

Miles per hour Kilometres per hour

A timeslip prints mph at almost every strip in the world, but a speedo or a data logger may not. A mph is 1.609344 km/h exactly.

Weight and power in, quarter mile time and trap speed out, by all three of the classic formulas.

Race Weight (lb) *

The car as it crosses the line: kerb weight plus the driver, the fuel in it and anything still in the boot.

Power (hp, bhp) *

Power Measured At

The formulas were fitted to flywheel power, so a wheel figure is grossed back up before they are applied.

Drivetrain Loss (%)

Only used when the figure above is a wheel number. Roughly 12% through a manual, 15 to 20% through an automatic or all four wheels.

Widget