Horsepower Calculator
Quarter-Mile & Torque/RPM Methods
Estimated Horsepower
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Ready for Calculation
Choose a method above and enter your values to estimate horsepower.
Two Ways to Estimate Horsepower
Horsepower can't always be measured directly without a dynamometer, but two well-known formulas let you estimate it from data you can actually gather: your quarter-mile trap speed, or your engine's torque curve at a given RPM.
Trap Speed Method
HP = Weight × (Trap Speed ÷ 234)³. This formula estimates flywheel horsepower from the vehicle's weight and its speed crossing the quarter-mile finish line — a classic drag-racing rule of thumb.
Torque & RPM Method
HP = Torque × RPM ÷ 5,252. This is the exact mechanical relationship between torque and horsepower — the two curves always cross at 5,252 RPM on a dyno chart.
Horsepower vs. Torque
Torque is the twisting force an engine produces; horsepower is the rate at which that work is done over time. A high-torque, low-RPM engine and a low-torque, high-RPM engine can produce identical horsepower figures but feel completely different to drive.
Estimates, Not Certified Numbers
Both formulas are widely-used approximations. A dynamometer test is the only way to get a certified, repeatable horsepower figure.
Key Takeaways
- Weight Matters: The trap speed method is sensitive to total vehicle weight, including the driver and any cargo — weigh the car as raced for accuracy.
- Peak vs. Curve: The torque/RPM method gives horsepower at one specific RPM — an engine's peak horsepower usually occurs at a higher RPM than peak torque.
- Drivetrain Loss: Both methods estimate flywheel/crank horsepower, which is typically 15-20% higher than what's measured at the wheels.