W/kg, kW/kg, PS per tonne and hp per tonne
Power to Weight Ratio Calculator
Cyclists use W/kg, car magazines use bhp per tonne, and spec sheets use PS or kW. This calculator reads power and weight in whichever units you have and returns every common power-to-weight figure.
- kW per kg
- 0.188 kW/kg
- PS per tonne
- 255 PS/t
- hp per lb
- 0.1141 hp/lb
- kg per kW
- 5.33 kg/kW
The formula and the units
Power-to-weight is power divided by mass. In SI that is watts per kilogram (W/kg). For the preset of 300 kW and 1,600 kg the answer is 188 W/kg, or 251 hp per tonne. One mechanical hp is 745.7 W and one PS is 735.5 W.
Conversions between ratios
| From | To | Multiply by |
|---|---|---|
| W/kg | hp per tonne | 1.341 |
| W/kg | PS per tonne | 1.359 |
| hp per tonne | W/kg | 0.7457 |
| kW/kg | W/kg | 1,000 |
Where it applies
Power-to-weight is used for cars, motorcycles, aircraft and cycling. For cars, ratios over 250 hp per tonne usually mean a genuine performance machine. See the hp to weight ratio calculator for imperial presentation.
Frequently asked questions
How do I calculate power to weight ratio?
Divide power by mass. In W/kg, use watts and kilograms.
Is higher power-to-weight always better?
For acceleration, yes. For handling, traction, braking and gearing also matter.
What is the difference between kW/kg and W/kg?
They are the same measure scaled by 1,000, so 0.3 kW/kg is 300 W/kg.
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