Engine Horsepower Calculator guide
Engine Horsepower Calculator: From Quarter-Mile Times
Use our engine horsepower calculator to estimate a car's horsepower from its weight and quarter-mile trap speed or elapsed time.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
Drag racers have long estimated engine power from quarter-mile results. Our Engine Horsepower Calculator uses the classic formulas.
How to use the calculator (Engine Horsepower Calculator)
- Enter the vehicle weight, including the driver.
- Choose whether you know the trap speed (mph at the end of the quarter mile) or the elapsed time.
- Enter the value.
The formulas
These come from Roger Huntington's work in the 1960s, with weight in pounds:
- Trap speed method: hp = weight × (trap speed ÷ 234)³
- Elapsed time method: hp = weight × (5.825 ÷ ET)³
The trap-speed method is usually more reliable, because it's less affected by wheelspin at the start.
Wheel and engine power
The result is roughly the power at the wheels. Some power is lost through the gearbox and drivetrain, usually 15–20%, so the engine (flywheel) figure is higher.
A worked example
With the calculator's default settings, a 1,500kg car with a trap speed of 105 mph makes about 299 wheel horsepower, or roughly 350 to 375 bhp at the engine.
Frequently asked questions
How accurate is it?
It's a ballpark figure. Aerodynamics, gearing, traction and weather all play a part. A rolling road (dyno) gives an accurate measurement.
Where can I do a quarter-mile run?
Only on a licensed drag strip or track day, never on public roads.
To convert torque and rpm to horsepower, use our Horsepower Calculator.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.