Calculators · Vehicle

Power-to-weight and torque-to-weight calculator

Power-to-weight ratio says more about how quick a vehicle feels than power alone: a light car with modest power can out-accelerate a heavy one with far more. These calculators give power-to-weight and weight-to-power in several units, torque-to-weight for pulling and low-speed performance, and the power needed to reach a target ratio.

Power-to-weight ratio

Divides power by mass and also shows the inverse, weight per unit of power. Use kerb weight for comparison with published figures, or add passengers and load for real-world numbers.

Results
Power-to-weight—kW/tonneKilowatts per tonne of mass.
Power-to-weight—hp/tonneHorsepower per tonne of mass.
Weight-to-power—kg/hpKilograms each horsepower has to move — lower is quicker.
Weight-to-power—lb/hpPounds each horsepower has to move.

Formula
kW/t = P / (m / 1,000)
kg/hp = m / (P / 0.7457)

Torque-to-weight ratio

Torque per tonne describes pulling ability at low speed — how easily a vehicle moves off, climbs a hill or tows. It is especially useful for trucks, tractors and off-road vehicles.

Results
Torque-to-weight—Nm/tonneNewton-metres per tonne of mass.
Weight-to-torque—kg/NmKilograms per newton-metre — lower pulls more easily.

Formula
Nm/t = T / (m / 1,000)

Power needed for a target ratio

Works backwards from a target power-to-weight ratio to the power a vehicle of a given mass would need. Useful when planning an engine upgrade or comparing against a benchmark car.

Results
Power required—Power needed to reach the target ratio.

Formula
P = target × (m / 1,000)

Worked example: a 150 kW family car

  1. 150 kW and 1,500 kg: 150 / 1.5 = 100 kW per tonne.
  2. 150 kW = 201 hp, so each horsepower moves 1,500 / 201 = 7.5 kg.
  3. To reach 120 kW/tonne at the same weight you would need 180 kW.

Typical power-to-weight ratios

Vehicle typePower-to-weight
Fully loaded heavy truck (40 t)about 8 – 12 kW/tonne
Economy carabout 50 – 70 kW/tonne
Family carabout 70 – 100 kW/tonne
Hot hatchabout 120 – 170 kW/tonne
Sports carabout 200 – 300 kW/tonne
Supercarabout 350 – 500 kW/tonne

Related

Torque, power and BMEP calculatorGear ratio, road speed and wheel torque calculatorCar specificationsCar rankings

About these results

Results are theoretical estimates from standard engineering formulas. Real-world figures depend on conditions these formulas do not capture. Always follow the manufacturer's specifications for maintenance, loading and safety decisions.

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