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Horsepower to Weight

Free Horsepower to Weight calculator with clear step-by-step results.

About Horsepower to Weight

Power-to-weight is the ratio that actually predicts acceleration, and it should be measured at the wheels with the car loaded as you drive it. Drivetrain losses of 12-18% are typical, and adding occupant weight to kerb weight moves the figure more than most people expect on a light car.

Formulas

Power at the wheels

Wheel hp = crank hp x (1 - drivetrain loss)

Power to weight

hp per tonne = wheel hp / total weight kg x 1000

Worked example

With the default values below, Horsepower to Weight returns Power to weight at the wheels of 147.83. Change any input above and every figure here is recalculated in your browser.

Inputs used

Engine powerminimum 1 hp
280 hp
Kerb weightminimum 1 kg
1,450 kg
Occupants and cargominimum 0 kg
160 kg
Drivetrain lossaccepts 0–40 %
15 %

Results

Power to weight at the wheels
147.83 hp/t
Weight carried per horsepower
6.765 kg/hp
Power at the wheels
238.0 hp
Power to weight in metric units
110.23 kW/t

Step by step

  1. 1Values used
  2. 2Power at the wheels
  3. 3Power to weight
  4. 4Power to weight at the wheels= 147.83 hp/t
  5. 5Weight carried per horsepower= 6.765 kg/hp
  6. 6Power at the wheels= 238.0 hp
  7. 7Power to weight in metric units= 110.23 kW/t

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What ratio counts as fast?

Around 100 hp per tonne is brisk, 200 is genuinely quick and 400 or more is supercar territory. Traction and gearing set the limit long before power does at the top end.

Front or rear wheel drive - does loss differ?

Yes. A transverse front-wheel-drive layout typically loses 10-13%, a longitudinal rear-drive 14-17% and all-wheel drive 18-22% because more gearsets are in the path.

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