🏎️ Power-to-Weight Calculator
Enter power (hp or kW) and weight (kg or lb) to get the power-to-weight ratio in hp/tonne, W/kg, hp/lb and kW/tonne.
200
hp/tonne
149.1
W/kg
0.09072
hp/lb
149.1
kW/tonne
Power-to-weight ratio is how much power moves each unit of mass, the best single predictor of acceleration. It's shown here as hp per tonne, watts per kilogram, hp per pound and kW per tonne. A hot hatch is around 150 hp/tonne; a supercar 400+; and cycling power is compared in W/kg. 🔒 In your browser.
How the power-to-weight calculator works
Power-to-weight ratio divides an engine's power by the vehicle's mass, how much power there is to move each unit of weight. The tool converts your inputs to consistent units and reports the ratio four common ways: horsepower per tonne, watts per kilogram, horsepower per pound and kilowatts per tonne. A higher ratio means quicker acceleration for a given aerodynamic and traction limit. A quick worked example: 200 kW in a 1,400 kg car is 200,000 ÷ 1,400 ≈ 143 W/kg, or about 191 hp per tonne. To compare cars fairly, keep the units matched, power in one unit over mass in one unit, since an "hp per pound" figure and a "W/kg" figure describe the same car with very different-looking numbers.
Power-to-weight predicts acceleration better than raw power alone, a light car with modest power can out-accelerate a heavy, powerful one. Use kerb (unladen) weight for comparisons, and remember real-world acceleration also depends on traction, gearing, aerodynamics and where in the rev range the power arrives. Cyclists and runners compare fitness the same way, in W/kg.
Frequently asked questions
How do you calculate power-to-weight ratio?
Divide power by weight in consistent units: a 300 hp car weighing 1,500 kg is 300 ÷ 1.5 = 200 hp per tonne. The tool also gives W/kg, hp/lb and kW/tonne.
What is a good power-to-weight ratio?
Roughly: an economy car is 60-90 hp/tonne, a hot hatch around 150, a sports car 200-300, and a supercar 400+. Higher means quicker acceleration, other things being equal.
Why does power-to-weight matter more than horsepower?
Because acceleration depends on force relative to mass. A light car with less power can beat a heavy, powerful one, which is why lightweight track cars feel so fast despite modest engines.
What weight should I use?
Kerb (unladen) weight for like-for-like comparisons, or add passengers and cargo for a real-world figure. Adding weight lowers the ratio and dulls acceleration noticeably.
What is a good W/kg for cycling?
Cyclists compare sustained power in watts per kilogram: recreational riders are around 2-3 W/kg, strong amateurs 4, and professional riders can hold 5-6 W/kg for long efforts. It's the same ratio idea applied to the rider.
How do I convert hp per tonne to watts per kilogram?
One horsepower is 745.7 W and a tonne is 1,000 kg, so W/kg = hp-per-tonne × 745.7 ÷ 1000 ≈ hp-per-tonne × 0.7457. A car at 200 hp/tonne is about 149 W/kg. The tool shows every unit at once, so you don't have to convert by hand.
Does power-to-weight predict top speed?
Not directly, top speed is mostly limited by aerodynamic drag, which rises with the square of speed, so it depends on power and the car's drag rather than weight. Power-to-weight predicts acceleration; a light car and a heavy one with the same power can reach a similar top speed but accelerate very differently.