Calculating Horsepower from Drag Racing
Horsepower is a unit of measurement for power, the rate at which work is done. In automotive terms, it's a key indicator of a car's performance potential. While a dynamometer is the most accurate way to measure horsepower at the wheels, you can get a surprisingly good estimate using data from a quarter-mile drag race.
The Formula
The calculation is based on a formula developed by Patrick Hale, which relates a vehicle's weight and its elapsed time (ET) over a quarter-mile to its horsepower. The formula assumes that the primary factor limiting acceleration over this distance is the engine's power output relative to the vehicle's mass.
Horsepower = (Weight / (ET / 5.825)³)
- Weight: The total weight of the vehicle in pounds, including the driver and any cargo.
- ET (Elapsed Time): The time in seconds it takes for the vehicle to travel a quarter-mile (1320 feet) from a standing start.
Important Note: This formula provides an estimate of flywheel horsepower, not horsepower at the wheels. It's a useful tool for comparison but doesn't account for factors like drivetrain loss, traction, aerodynamics, or driver skill, which can all affect the actual quarter-mile time.