Power-to-Weight Calculator
Enter peak power and vehicle weight (curb or with driver). Compare cars with hp/tonne, kW per kilogram, and imperial hp/lb — useful for performance shopping, not a substitute for timed testing.
Calculate
Calculate
Measurements convert when you switch units
Result
The formula
Power-to-weight is engine output divided by mass. We convert your power unit to kilowatts and horsepower, convert weight to kilograms and pounds, then report several common ratios so metric and imperial readers can compare the same car.
Worked example
- 300 hp, curb weight 1,450 kg
- Tonnes = 1,450 ÷ 1,000 = 1.45 · hp/tonne = 300 ÷ 1.45 ≈ 206.9
- kW ≈ 300 × 0.7457 ≈ 223.7 · kW/kg ≈ 0.154
Result: ≈ 207 hp/tonne · 0.154 kW/kg
How power-to-weight is calculated
The ratio is only as honest as the inputs. Brochure horsepower, DIN vs SAE ratings, and whether weight includes fluids, options, and a driver all change the number.
Power units
Mechanical horsepower (hp), metric horsepower (PS / CV), and kilowatts are related by fixed factors: 1 hp ≈ 0.7457 kW and 1 PS ≈ 0.7355 kW. European brochures often quote PS or kW; US materials usually quote SAE hp.
Which weight?
Curb weight is the empty car with fluids. For strip or road feel, add fuel, passengers, and cargo. Race classes sometimes use minimum weight with driver — match the definition you care about.
What we do not model
No drivetrain loss, boost, altitude, tire grip, or aero. Two cars with the same P/W can feel very different once gearing and traction enter the picture.
Interesting facts
Tonne vs ton
Metric hp/tonne uses 1,000 kg. US “hp per ton” often means a short ton (2,000 lb). This tool labels both so you do not mix them.
Supercars vs hot hatches
Many modern hot hatches land near 150–200 hp/tonne; supercars and light track cars often clear 300+ hp/tonne at curb weight.
Electric motors
EVs quote peak electrical or motor power that may not be sustained. Peak P/W can look huge relative to the continuous rating you actually use on a highway pull.
Power alone misleads
A heavier car with more horsepower can still out-accelerate a lighter, weaker car — but at equal power, less mass almost always helps.
Frequently asked questions
Divide power by mass. For hp/tonne, convert kilograms to tonnes (÷ 1,000) then divide horsepower by that mass. We also show kW/kg and hp/lb from the same inputs.
Use curb weight for brochure comparisons. Add ~75–100 kg (or your actual driver + fuel) when estimating real-world punch.
Not exactly. 1 PS (metric horsepower) is about 0.986 hp, or ≈ 0.7355 kW. Select the unit that matches your power figure.
Everyday cars may sit under ~100 hp/tonne; sporty models often 150–250; dedicated performance cars go higher. Context and gearing matter more than a single cutoff.
No — enter crank or wheel horsepower consistently. Mixing crank hp with race weight (or vice versa) skews comparisons.
References
- Horsepower and related power units Unit relationships for mechanical horsepower and SI watt.
- Vehicle mass definitions (curb / gross) Regulatory context for how vehicle mass is reported.