How to use this calculator
- Enter or choose power.
- Enter or choose body weight.
- Enter or choose weight in.
- Enter or choose target power-to-weight.
- The power-to-weight updates as you type. Use Copy result or Share to keep it.
Method
W/kg = Power ÷ Body mass (kg); Power for target = Target × Mass; Mass for target = Power ÷ Target
- Power
- sustained output in watts
- Mass
- rider body mass (1 lb = 0.45359237 kg)
Worked example
- 250 W ÷ 70 kg = 3.57 W/kg.
- 4 W/kg at 70 kg needs 4 × 70 = 280 W.
- At 250 W, 4 W/kg would mean 250 ÷ 4 = 62.5 kg.
A 70 kg rider holding 250 W produces 3.57 W/kg; reaching 4 W/kg takes another 30 W.
What the result means
W/kg compares riders of different sizes on climbs. On flat roads absolute watts and aerodynamics matter more, so a heavier rider with lower W/kg can still be faster.
Assumptions and limits
- Body weight only; the bike’s weight is not included.
- Power is a sustained figure from the same kind of test each time.
- Losing weight to raise W/kg can also cost power; any weight-loss plan should be discussed with a qualified professional.
Questions
Should I include the bike in the weight?
Convention is body weight only. Total system weight matters for climbing-speed estimates, which need a separate physics model.
Which power figure should I use?
Use the same duration each time, for example your FTP or best 20-minute power, so that comparisons are fair.