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Power-to-Weight Ratio Calculator

Find your power-to-weight ratio.

How it is calculated

Power is entered in kilowatts (kW) and weight in kilograms (kg). The tool gives two figures. Watts per kilogram is W/kg = power × 1000 / weight. Horsepower per tonne is hp/t = power × 1.34102 / (weight / 1000), where 1.34102 is the number of mechanical horsepower in one kilowatt.

Weight must be above zero. Use the weight that matches the situation: a car's kerb weight, or rider plus bike for cycling. A higher ratio means more power for each kilo it has to move, which generally means stronger acceleration. It does not account for gearing, traction or aerodynamics, so it is a comparison figure, not a performance guarantee.

Worked example

A car makes 150 kW and weighs 1,200 kg. W/kg is 150 × 1000 / 1200 = 125.00 W/kg. For horsepower per tonne, convert the power: 150 × 1.34102 ≈ 201.15 hp. The weight in tonnes is 1.2, so 201.15 / 1.2 = 167.63 hp/t.

Try this example →

Common mistakes

  • Entering horsepower in the kW field. Divide hp by 1.341 first, or the W/kg result will be about 34% too high.
  • Entering weight in tonnes or pounds; the field expects kilograms.
  • Comparing a figure that uses kerb weight with one that includes driver and fuel.
  • Using peak crank power for one vehicle and wheel power for another; the numbers are not directly comparable.

About this calculator

This calculator divides output power by total weight to give the power-to-weight ratio — a single number that says how much thrust or acceleration is available for each kilogram being moved, usually expressed in watts or horsepower per kilogram.

It is the number racers actually care about: cyclists compare watts per kilogram to gauge climbing ability, motorsport engineers use hp/kg to compare cars regardless of size, and aircraft designers use it to judge climb performance. A lighter vehicle or rider with the same power always wins on power-to-weight.

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Comments (1)

  • Editorial team

    The power box takes kilowatts, so convert first if your figure is in horsepower: one mechanical horsepower is about 0.7457 kW, and the metric PS used on many European spec sheets is about 0.7355 kW. For cycling, enter watts as kilowatts, so 250 W is 0.25, and use rider plus bike: 0.25 kW over 78 kg is 3.21 W/kg. Is your weight figure kerb weight, or does it include fuel and driver? Tell us what you're comparing.

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