HP to MPH Calculator
Estimate a vehicle's top speed in MPH from its horsepower and weight.
This calculator estimates the speed a vehicle can reach from its horsepower and weight, based on the same physics that links power to quarter-mile trap speed. It's a useful guide to a car's performance potential.
HP to MPH Formula
Speed rises with the cube root of the power-to-weight ratio, which is why doubling horsepower doesn't double speed — aerodynamic drag rises sharply as speed increases. This estimates trap speed rather than absolute top speed, which is also limited by gearing and drag.
How to Use This Calculator
- Enter horsepower.
- Enter vehicle weight in pounds.
- Read the estimated speed.
Worked Example
For the reverse — estimating horsepower from a known speed — see the trap speed HP calculator.
Frequently Asked Questions
Use MPH = 234 × (HP ÷ Weight)^(1/3). It estimates quarter-mile trap speed, which closely tracks a car's performance potential.
Because aerodynamic drag rises with the square of speed, and speed scales with only the cube root of power-to-weight. Big speed gains need large power increases.
It estimates quarter-mile trap speed. True top speed also depends on gearing, aerodynamics, and how long a road you have.
Yes, through power-to-weight ratio. A lighter car reaches a given speed with less power, though at very high speeds aerodynamic drag dominates over weight.
It's a guide, typically within about 5% for a conventional car. Aerodynamics, gearing, and drivetrain losses cause the variation.