Power-to-Weight Ratio
Watts per kilogram and horsepower per tonne and per pound, from any units you enter.
Three formats at once
Enter power in hp, kW, or W and weight in kg, lb, or tonnes — get W/kg, hp/tonne, and hp/lb together.
Compare fairly
Because it divides out weight, the ratio compares vehicles or athletes of different sizes on equal terms.
What is power-to-weight ratio?
Performance in a single number
Power-to-weight ratio is how much power you have for every unit of weight you must move. It is one of the best single predictors of acceleration and climbing performance, because two machines with the same power perform very differently if one is far lighter. Cyclists track it in watts per kilogram; motorsport uses horsepower per tonne or per pound.
The ratio is just power divided by weight. The only care needed is keeping units consistent, which the calculator handles using exact conversion factors from standards bodies such as NIST.
ratio = power ÷ weightTo convert, 1 horsepower ≈ 745.7 W and 1 kW = 1,000 W; 1 lb ≈ 0.4536 kg and 1 tonne = 1,000 kg. The calculator converts your power to watts and your weight to kilograms, divides, and then expresses the result in all three common formats.
Take a 300 hp car weighing 1,500 kg.
Convert power to watts
300 hp × 745.7 = 223,710 W.Divide by weight in kg
223,710 ÷ 1,500 = 149.1 W/kg.Express in hp per tonne
300 hp ÷ 1.5 tonnes = 200 hp/tonne.Express in hp per pound
300 hp ÷ 3,307 lb = 0.091 hp/lb (about 11 lb per hp).
The benchmarks differ by domain, but the principle is the same: higher is quicker.
Cycling (W/kg)
~2–3 recreational, 3.5–4.5 strong amateur, 5.5–6.5+ elite professional, at threshold power.
Cars (hp/tonne)
~80–120 family car, 150–200 hot hatch, 250–350 sports car, 400+ supercar.
Cars (lb/hp)
Below ~10 lb per horsepower marks genuinely fast acceleration.
Because the ratio already divides out weight, it lets a small rider and a large rider — or a light car and a heavy one — be compared on equal footing, which raw power never allows.
A higher number means more performance per unit of mass. The W/kg figure is the universal one and the standard in cycling; the horsepower-per-tonne and per-pound figures are the everyday language of car performance. Remember that improving the ratio works from both ends: adding power and removing weight help equally, and shedding mass also sharpens braking and cornering. Compare a few scenarios — for instance, the same engine in a lighter chassis — to see how much the denominator matters.
Power-to-weight is powerful but partial.
One factor among many
The ratio is mathematically exact for the numbers you enter, but real-world performance also depends on aerodynamics, gearing, traction, drivetrain losses, tyre grip, and rolling resistance. Two machines with the same power-to-weight can still differ markedly in acceleration and top speed. Treat the ratio as a strong comparative benchmark, not a complete prediction of how something will perform.