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.
Trap Speed vs True Top Speed
This calculator estimates quarter-mile trap speed — the speed at the end of a standing 1,320-foot run — not a car's absolute top speed. Top speed is set by where aerodynamic drag finally balances available power, plus gearing limits, and usually occurs well beyond the quarter mile. Trap speed is the better proxy for engine power because it reflects the energy the car built up over a fixed distance.
Why Speed Scales With the Cube Root of Power
Aerodynamic drag rises with the square of speed, and the power needed to overcome it rises with the cube. That's why the formula uses the cube root of power-to-weight: doubling horsepower only raises trap speed by about 26%, not 100%. Weight reduction helps acceleration more than top-end speed, where drag dominates.
Estimated Trap Speed (3,200 lb car)
| Horsepower | Est. Trap Speed |
|---|---|
| 200 | 93 MPH |
| 300 | 107 MPH |
| 400 | 117 MPH |
| 600 | 134 MPH |
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.