The ratio, in whichever units you use
Power-to-weight ratio is just power divided by mass. Cars are usually quoted in horsepower per pound; cyclists and engineers use watts per kilogram. Higher means quicker acceleration for the same drag.
To move between them: 1 hp/lb = 1,644 W/kg. Power converts as 1 hp = 745.7 W, mass as 1 lb = 0.4536 kg.
Where vehicles and riders land
| Class | hp/lb | W/kg |
|---|---|---|
| Family sedan | 0.04–0.06 | 65–100 |
| Sports car | 0.09–0.13 | 150–210 |
| Supercar | 0.15–0.25 | 250–410 |
| Litre-class superbike | 0.30–0.40 | 490–660 |
| Formula 1 | ~0.59 | ~970 |
A 600cc sports bike (about 0.30 hp/lb) out-accelerates most supercars: it makes far less power, but carries far less weight. That is why the ratio, not raw power, predicts launch.
Cyclists use the same number for their body
| Rider level | W/kg (at threshold) |
|---|---|
| Recreational | 1.5–2.5 |
| Competitive amateur | 3.0–3.5 |
| Strong amateur / climber | 4.0–4.5 |
| Professional | 5.6–6.4+ |
- Use threshold power, not average. The figure comes from FTP, the power you can hold for about an hour, divided by body weight in kg. Casual training averages read lower.
- Curb weight for cars. Quote the empty kerb weight, not the loaded one. Add fuel, passengers and cargo and the real ratio drops.
- Ratio is acceleration, not top speed. A high ratio launches hard, but maximum speed is set by aerodynamics and gearing, not by this number alone.
Common questions
How do you calculate power-to-weight ratio?
Divide power by mass. In metric terms that is watts divided by kilograms; for cars it is often horsepower divided by pounds. A 300 hp car at 3,000 lb is 0.10 hp/lb.
What is a good power-to-weight ratio for a car?
It depends on the type. A family sedan sits near 0.04 to 0.06 hp/lb, a sports car around 0.10 to 0.15, and a supercar above 0.15. Formula 1 reaches roughly 0.6 hp/lb.
What does watts per kilogram mean for a cyclist?
It is functional threshold power divided by body weight. A fit amateur is around 3 to 3.5 W/kg; Tour de France riders sustain 5.6 to 6.4 W/kg. It is what decides who drops whom on a climb.
