Power-to-weight ratio formulas
The inverse view is weight ÷ power. A 1,500 kg car with 300 metric hp therefore produces 200 PS/tonne and 5 kg/PS.
BHP, metric horsepower and kilowatts are not identical
Mechanical horsepower, often labelled bhp in vehicle specifications, equals approximately 745.7 watts. Metric horsepower, also written PS, ch or CV depending on the country, equals approximately 735.5 watts. One kilowatt equals 1,000 watts.
The calculator first converts every power entry to kilowatts. That prevents a comparison from silently treating 300 bhp and 300 PS as the same output.
Power-to-weight comparison examples
| Power | Weight | kg/PS | PS/tonne | kW/tonne |
|---|---|---|---|---|
| 100 PS | 1,000 kg | 10.00 | 100.0 | 73.5 |
| 150 PS | 1,200 kg | 8.00 | 125.0 | 91.9 |
| 200 PS | 1,400 kg | 7.00 | 142.9 | 105.1 |
| 300 PS | 1,500 kg | 5.00 | 200.0 | 147.1 |
What is a good power-to-weight ratio for a car?
There is no universal pass mark. A city car, tow vehicle, classic car, electric SUV and track-focused sports car serve different purposes. Compare vehicles from a similar category and era before calling one result good or poor.
Vehicle mass can also be published as kerb weight, DIN weight, EU mass in running order or measured weight. A fair comparison uses the same definition on both sides.
Why the ratio cannot predict a trustworthy 0–60 mph time
At launch, driven wheels, tyre grip, gear ratios, shift speed and electronic control matter enormously. At higher speed, aerodynamic drag and the shape of the power curve become more important.
Sources and checks
AutoPrisme uses the figures you enter. The links below explain the rule, market context or consumer protections used to frame this calculator. Always verify the numbers in your own quote or contract.
- NIST Guide to the SI — power conversion factorsReference conversion factors for mechanical, metric and UK horsepower to watts.
- NIST Guide to the SI — alphabetical conversion tableReference factors used to distinguish horsepower units and convert mass and torque-related inputs.
Frequently asked questions
How do you calculate power-to-weight ratio?
Divide power by vehicle mass in tonnes to obtain horsepower or kilowatts per tonne. Divide mass by power for kg per horsepower or pounds per bhp.
Is a higher power-to-weight ratio better?
For performance potential, more power per unit of mass is generally favourable. In the inverse kg-per-hp or lb-per-bhp format, a lower number is favourable.
What is the difference between bhp, metric hp and kW?
They are different power units. One mechanical horsepower is about 745.7 W, one metric horsepower or PS is about 735.5 W, and one kilowatt is 1,000 W. The calculator converts them before comparing vehicles.
Should driver and passenger weight be included?
For catalogue comparisons, use the same published mass convention for both cars. For a real-use comparison, add occupants and luggage consistently to both vehicles.
Can power-to-weight ratio predict 0–60 mph?
Not reliably on its own. Traction, gearing, shift time, torque delivery, tyres, aerodynamics and launch conditions can create very different acceleration times at the same ratio.
Does torque-to-weight ratio matter?
It adds context about torque relative to mass, but wheel torque also depends on gear ratios and final drive. It should not be interpreted as a direct acceleration result.