Quick answer: Power-to-weight ratio = power ÷ weight. A 228 hp car weighing 2,833 lb has 228 ÷ 2,833 = 0.0805 hp/lb, the same as 161 hp per US ton or 12.43 lb per hp. Higher hp per ton means quicker acceleration.
The power-to-weight ratio formula
ratio = power ÷ weightSame machine, different units: 0.0805 hp/lb = 161 hp/ton = 12.43 lb/hpA 228 hp sports car at 2,833 lb
- 228 ÷ 2,833 = 0.0805 hp/lb
- × 2,000 = 161 hp per US ton
- 2,833 ÷ 228 = 12.43 lb per hp
- 170 kW ÷ 1,285 kg ≈ 132 W/kg
Result: 161 hp per ton
The power-to-weight ratio is often given in W/kg by engineers as a unit-independent figure.
Power-to-weight units and how they convert
| Unit | Used by | Meaning |
|---|---|---|
| hp per US ton | US car reviews | hp for every 2,000 lb |
| hp per lb | Drag racing | hp for every pound |
| lb per hp | US enthusiasts | Pounds per hp (lower is better) |
| hp per tonne | UK and EU reviews | hp for every 1,000 kg |
| kg per hp | Metric enthusiasts | Kilograms per hp (lower is better) |
| W/kg | Cycling, engineering | Watts for every kilogram |
Why power-to-weight beats horsepower alone
A heavy car with a big engine can be slower than a light car with a modest one. The ratio captures both halves of that trade-off.
Car A vs Car B
- Car A: 400 hp, 4,000 lb = 200 hp/ton
- Car B: 300 hp, 2,600 lb = 231 hp/ton
Result: Car B usually accelerates harder
Typical power-to-weight ratios
| Vehicle type | hp per ton | hp per lb |
|---|---|---|
| Economy commuter | 85 – 110 | 0.04 – 0.06 |
| Warm hatch, sports sedan | 130 – 180 | 0.07 – 0.09 |
| Sports car | 180 – 300 | 0.09 – 0.15 |
| Supercar | 350 – 500 | 0.18 – 0.25 |
| Hypercar | 650 – 700 | 0.30 – 0.34 |
| Litre-class sport motorcycle | 700 – 900 | 0.35 – 0.45 |
For cyclists, recreational riders hold about 2 to 3 W/kg for an hour, strong amateurs 4 to 4.5 and professionals 5.5 to 6.5.
Tips for an accurate ratio
- Use curb weight, not dry weight, for road cars.
- Compare crank to crank or wheel to wheel horsepower.
- Add the rider’s weight for bikes and motorcycles.
- Compare in the same units.
Frequently asked questions
What is a good power-to-weight ratio?
For a road car, about 130 to 180 hp per ton feels lively and above 300 hp per ton is supercar territory. The right ratio depends on what the machine is for.
How do I calculate weight to horsepower?
Divide weight by horsepower. A 3,000 lb car with 250 hp carries 12 lb per hp; lower is quicker.
What is the difference between hp per ton and lb per hp?
They are inverses. hp per ton is higher-is-faster; lb per hp is lower-is-faster.
Should I use crank or wheel horsepower?
Either, as long as you are consistent. Wheel horsepower is lower after drivetrain losses.
How do I get W/kg?
Multiply horsepower by 745.7 for watts and divide by weight in kg. 228 hp on 1,285 kg is about 132 W/kg.
Does adding weight always hurt the ratio?
Yes, unless power rises too. That is why builders remove weight, which is often cheaper than adding power.
Related tools
Accuracy note: Every conversion is re-derived from the formula. Manufacturer weights and outputs vary by trim and measurement method, so confirm critical figures against official specifications.
Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.