What is the trap-speed horsepower method?
This calculator uses the classic drag-racing formula that estimates a vehicle’s flywheel horsepower from its weight and the speed it reaches at the end of a quarter mile (the ‘trap speed’). It’s a popular rule-of-thumb used by racers and enthusiasts to get a quick horsepower ballpark without a dyno.
How this calculator works
The formula is: Horsepower = Weight × (Trap Speed ÷ 234)3, where weight is in pounds (including the driver) and trap speed is in mph. This empirical relationship was derived from observed drag-strip data correlating terminal speed with power-to-weight ratio.
This method assumes a well-driven vehicle with good traction and a typical drivetrain — it does not account for aerodynamic drag, gearing, tire grip, or driver skill, so real dyno numbers can differ noticeably, especially for very light or very aerodynamic vehicles.
Use this tool for general estimation and educational purposes only, not as a substitute for an actual dynamometer test.