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Power-to-Weight Ratio Calculator (W/kg)
Power-to-weight is your power in watts divided by your body weight in kilograms. Example: 216 W at 72 kg is 3.0 W/kg. Enter your numbers below, work out the watts you need for a target, and see what your W/kg means on Alpe d'Huez, Mont Ventoux and the Tourmalet.
Your power-to-weight
What it means on a real climb
Estimated times at your W/kg × body weight, with an 8 kg bike, by our model:
- Alpe d'Huez (13.8 km, 1,120 m): 1:14
- Mont Ventoux (21.8 km, 1,617 m): 1:49
- Col du Tourmalet (19 km, 1,404 m): 1:34
This page is about cycling. For cars, power-to-weight is usually given in hp per tonne.
Questions
Does bike weight count?
Not in W/kg: power-to-weight uses your body weight. Climbing speed, though, depends on everything you lift, so the climb times below use rider + bike + kit.
How much faster is 1 kg lighter?
By our model, a 72 kg rider on an 8 kg bike at 216 W climbs Alpe d'Huez in 1:14:06. With 1 kg less in total it is 1:13:15, about 51 seconds faster.
Which power should I use?
For climbs, the power you can hold steadily for about an hour. Shorter efforts give higher numbers that you cannot keep up on a long climb.
How we calculate
Speed comes from a steady power balance on a constant grade: power × drivetrain efficiency = v × m × g × (sin θ + Crr × cos θ) + ½ × ρ × CdA × v³, where v is speed, m is rider + bike + kit, g = 9.80665 m/s², θ is the angle of the average grade, Crr is rolling resistance, ρ is air density and CdA is the drag area. We solve it for v, and time = distance ÷ v. No wind, no stops, steady power.
Our defaults are Crr 0.005, CdA 0.40 m², air density 1.15 kg/m³ and no drivetrain loss: the same assumptions as our gearing guide and the Angliru page, so the numbers on the site agree. You can change them under "Assumptions".
The model has the same structure as the road-cycling power model of Martin, Milliken, Cobb, McFadden and Coggan, "Validation of a mathematical model for road cycling power", Journal of Applied Biomechanics 14(3): 276–291 (1998). In that study, modelled and measured power agreed closely (R² = 0.97, standard error 2.7 W). Their test bike used Crr 0.0032 and a drivetrain efficiency of 97.698%, so their rider was faster than our more cautious defaults would predict. Leave efficiency at 1 to match the rest of this site.
More tools: Climb time calculator · Gear calculator