Power
Use whichever weight figure you have. Kerb weight, DIN weight and EU weight-with-driver can differ by 60-75 kg on the same car - see the note below the results for why.
Power-to-weight ratio
Rough performance bands
| Typical car | bhp/tonne | kW/tonne (W/kg) |
|---|---|---|
| City car | 60-80 | ~45-60 |
| Hot hatch | 150-200 | ~110-150 |
| Sports car | 250-350 | ~185-260 |
| Supercar | 400+ | ~300+ |
How the ratio is worked out
The formula is bhp/tonne = bhp ÷ (weight in kg ÷ 1000). Worked example: a 200 bhp car weighing 1400 kg has 1400 ÷ 1000 = 1.4 tonnes, so 200 ÷ 1.4 ≈ 142.9 bhp/tonne - this page's own defaults. In kW that's 200 × 0.7457 ≈ 149.1 kW, giving 149.1 ÷ 1.4 ≈ 106.5 kW/tonne. Because a tonne is exactly 1000 kg, kW/tonne and W/kg are the same number - 106.5 kW/tonne is also 106.5 W/kg - which is worth knowing if a figure is quoted either way without saying which.
Why power-to-weight predicts acceleration better than power alone
Accelerating a car means accelerating its whole mass, so what matters isn't raw power on its own but power relative to the mass being moved. A 300 bhp saloon weighing two tonnes and a 200 bhp sports car weighing 1.1 tonnes have very different bhp/tonne figures (150 versus roughly 182) despite the saloon having more power in absolute terms, and the lighter car will typically feel and accelerate the quicker of the two. That's why power-to-weight, not peak power, is the figure motorsport classes and reviewers reach for when comparing acceleration potential across different cars. It's still a simplification: gearing, traction, aerodynamics and how the power is delivered across the rev range all affect real-world acceleration too, so treat bhp/tonne as a strong indicator rather than a precise 0-60 predictor.
bhp/tonne vs kg/bhp conventions
This calculator gives the "power per mass" direction - bhp/tonne, kW/tonne and W/kg - which is the form most commonly quoted. Some racing series and homologation documents flip it around and quote kg/bhp (or kg/kW) instead, meaning weight per unit of power, where a lower number means a faster car. The two are simple reciprocals of each other: 1400 kg at 200 bhp is 142.9 bhp/tonne, or equivalently 7.0 kg/bhp (1400 ÷ 200). If you see a figure quoted as kg/bhp and want the bhp/tonne equivalent, divide 1000 by the kg/bhp number.
Why quoted weights differ (kerb/DIN/EU with driver)
Manufacturers don't all measure weight the same way, and the gap is large enough to move a bhp/tonne figure by a few points. Kerb weight typically means the car ready to drive with fluids topped up and a part-full tank, but whether it also includes an allowance for a driver depends on the standard used. DIN weight (a German convention) usually excludes the driver and uses a lower fuel fill. EU kerb weight, by contrast, often adds a nominal 75 kg driver on top. The practical effect is that the same car can be quoted at two different weights roughly 60-75 kg apart depending on which standard a spec sheet is using, neither of which is wrong - they're just different conventions. If you're not sure which one a figure uses, treat the resulting bhp/tonne as a reasonable estimate rather than an exact figure.
Related tools
Only have a PS or kW figure from a spec sheet and want it in bhp before typing it in here? The kW to bhp converter handles that conversion on its own. And if you're starting from a torque and rpm reading rather than a headline power figure, the torque and power converter turns that into bhp, PS or kW first. To turn that ratio into an estimated sprint time, try the 0-60 calculator.