Power-to-Weight Ratio Calculator
Power-to-weight ratio in the several forms it is quoted in, and a rough acceleration estimate.
Power-to-weight predicts acceleration better than power alone, which is why a light car with a modest engine can out-accelerate a heavy one with far more power.
How the power-to-weight ratio calculator works
Power-to-weight predicts acceleration better than power alone, which is why a light car with a modest engine can out-accelerate a heavy one with far more power.
It is quoted inconsistently. Europe uses kilowatts or horsepower per tonne; the US often uses pounds per horsepower, which runs the other way — lower is better. All are shown here so a figure from any source can be compared.
The 0–100 estimate is a rough empirical fit and nothing more. Real acceleration depends on traction, gearing, transmission losses and where in the rev range the power arrives; a figure from this can be out by a second either way.
Formula: ratio = power / mass
Worked examples
| Inputs | Power to weight | Note |
|---|---|---|
| 150 kW in a 1,450 kg car | 103.4 kW per tonne | 103 kW per tonne |
| The same car with four aboard | 103.4 kW per tonne | noticeably slower |
| Quoted in horsepower | 103.4 kW per tonne | the same car |
FAQFrequently asked questions
What is a good power-to-weight ratio?
Around 60–80 kW per tonne is an ordinary family car; 150 and above is genuinely quick; supercars exceed 300.
Why is pounds per horsepower backwards?
Because it is mass over power rather than power over mass, so a lower number is better. It is a US convention.
Does power-to-weight predict acceleration?
Better than power alone, but traction, gearing and where the power arrives in the rev range all matter. Treat the estimate here as rough.
Should I use kerb mass or loaded mass?
Kerb mass for comparing cars; loaded mass for what you will actually experience. Four adults and luggage is roughly 300 kg.
Do PS and hp differ?
Yes, by about 1.4%. PS is metric horsepower at 735.5 W; mechanical horsepower is 745.7 W.
Where these figures come from
- ISO 4000 / ETRTO — tyre designation and dimensions — the width / aspect ratio / rim marking this page decodes
- UK Vehicle Certification Agency — the official UK fuel and emissions data
Last checked: September 2026. Tyre dimensions follow the ISO metric marking standard; engine formulas are the standard textbook forms.