Power-to-weight ratio calculator

Compare a power figure and vehicle weight using three common power-to-weight formats.

Formulahorsepower per US ton = horsepower ÷ pounds × 2,000

Use matching definitions

Wheel horsepower and crank horsepower are different measurements, just as curb, dry and gross vehicle weight include different things. Comparisons are meaningful only when the inputs use the same basis.

A ratio does not predict a complete performance result

Traction, gearing, aerodynamics, torque curve, drivetrain loss and conditions also affect acceleration and speed.

Three ways of saying the same thing

A 300 hp car weighing 3,300 lb is 182 hp per US ton, or 11 pounds per horsepower, or 149 kW per tonne. All three describe one ratio; which you use depends on who you are talking to. Pounds per horsepower is the American shorthand, kilowatts per tonne the European one, and lower is better in the first while higher is better in the other two.

The comparison only holds if the inputs match. Crank horsepower against wheel horsepower flatters a car by roughly the drivetrain loss, often 10 to 15% on a manual, and kerb weight against dry weight can differ by 100 kg before anyone gets in.

Frequently asked questions

Should I use crank or wheel horsepower?

Either, as long as every car in the comparison uses the same one. Manufacturer figures are crank power, measured at the flywheel; a rolling-road figure is wheel power, measured after the drivetrain has taken its cut. Mixing them makes the car quoted at the crank look better than it is.

Which weight should I enter?

Kerb weight, meaning the car ready to drive with fluids, is the usual basis and the fairest for comparison. Dry weight leaves out fluids and flatters the number, and gross vehicle weight is the loaded maximum. Add the driver and a tank of fuel if you want the figure that matches how the car actually feels: 75 kg of driver on a light car moves the ratio noticeably.

What is a good power-to-weight ratio?

For context rather than as a target: a typical family hatchback sits near 80 to 100 hp per ton, a hot hatch around 150 to 200, and a serious sports car above 300. Motorcycles are in a different bracket entirely, because a 200 hp bike with rider weighs under half a tonne.

Does a better ratio mean a quicker car?

It is the strongest single predictor and still not the whole story. Traction decides whether the power reaches the road at all, gearing decides how much of the powerband you can use, and aerodynamics decides what happens at speed. A torquey engine with a flat curve can out-accelerate a peakier one on an identical ratio.

How do I convert kilowatts to horsepower?

One mechanical horsepower is 0.7457 kW, so multiply kW by 1.341 to get hp. Watch for metric horsepower, PS or CV, which is slightly smaller at 0.7355 kW: a car quoted at 300 PS is about 296 hp. The calculator accepts either power unit and converts internally.