About the Power-to-Weight Ratio Calculator
This power-to-weight ratio calculator shows how much power a vehicle has for every unit of weight it carries — the single best number for comparing straight-line performance between cars, motorcycles and even bicycles. Enter the power in horsepower, kilowatts or metric PS and the weight in pounds or kilograms, and it calculates horsepower per tonne, kilowatts per tonne, horsepower per US ton and the inverse figures, pounds per horsepower and kilograms per kilowatt.
Enthusiasts use it to compare a light, modest-power car with a heavy, powerful one, to see how much a weight reduction or tune is worth, and to understand why a 1,000 kg roadster can keep up with a much more powerful SUV. You can add the weight of the driver and passengers or cargo to see the ratio as the car is actually driven.
Use the manufacturer’s curb weight (with fluids, without occupants) for like-for-like comparisons, and crank horsepower as quoted by the maker. If you only have dyno wheel horsepower, convert it first, as wheel figures are lower because of drivetrain losses. Power-to-weight predicts acceleration well but ignores gearing, traction and aerodynamics.
With the default inputs, the horsepower per tonne is 189 hp/t. Change any value above to recalculate instantly.
How to use the power-to-weight ratio calculator
- 1Enter the engine power and pick hp, kW or PS.
- 2Enter the curb weight and pick pounds or kilograms.
- 3Optionally add driver, passenger and cargo weight.
- 4Read hp per tonne, lb per hp and the other ratios to compare vehicles.
Formula and method
The calculator converts the power to watts (1 hp = 745.7 W, 1 PS = 735.5 W, 1 kW = 1,000 W) and the weight to kilograms (1 lb = 0.45359237 kg), adding any occupant or cargo weight you enter. It then divides power by weight in each unit system.
Higher hp per tonne (or kW per tonne, W/kg) means quicker acceleration. Pounds per horsepower and kg per kW are the inverse — lower is better — and are popular in racing classes and US car magazines. A US ton is 2,000 lb, while a metric tonne is 1,000 kg (about 2,204.6 lb).
- P
- Engine power (converted to hp, kW and W)
- W
- Vehicle weight plus any payload
Worked examples
300 hp sports sedan weighing 3,500 lb
3,500 lb is 1,587.6 kg, so 300 hp ÷ 1.5876 t = 189 hp per tonne. The inverse is 3,500 ÷ 300 = 11.67 lb per hp, and per 2,000-lb US ton it is 171.4 hp.
Lightweight roadster: 135 kW and 1,050 kg
135 kW ÷ 1.05 t = 128.6 kW per tonne. 135 kW is 181 hp, which gives 172.4 hp per tonne or 12.79 lb per hp — close to the 300 hp sedan despite far less power.
Same sedan with a 180 lb driver
Adding 180 lb brings the total to 3,680 lb, so the ratio drops to 12.27 lb per hp, or about 180 hp per tonne.
Frequently asked questions
What is a good power-to-weight ratio for a car?+
Economy cars sit around 70–100 hp per tonne and mainstream family cars and SUVs roughly 90–150, hot hatches and sports sedans roughly 150–250, and supercars 400 hp per tonne or more. In pounds per horsepower that is roughly 15–30 lb/hp for ordinary cars and under 6 lb/hp for supercars.
How do I calculate pounds per horsepower?+
Divide the vehicle weight in pounds by its horsepower. A 3,200 lb car with 250 hp has 3,200 ÷ 250 = 12.8 lb per hp. Lower numbers mean each horsepower has less weight to move, so the car accelerates faster.
Should I use curb weight or gross weight?+
Use curb weight for comparing published specifications, because that is what manufacturers quote. Add the driver and any passengers or cargo to see the real-world ratio, which is especially significant for light cars and motorcycles.
What is the difference between hp, bhp and PS?+
Horsepower (hp) and brake horsepower (bhp) are usually the same mechanical horsepower of about 745.7 watts. PS (or CV) is metric horsepower, about 735.5 watts, so a figure in PS is roughly 1.4% larger than the same power in hp.
Does power-to-weight decide 0–60 times?+
It is the strongest single predictor, but traction, gearing, launch control, torque curve and drivetrain all matter. All-wheel-drive cars often beat rear-drive cars with similar ratios off the line.