Free Cycling Climb Calculator: Time, Power, VAM & W/kg

How to use the estimate

Enter the climb, your weight and your bike, then either the average power you expect to hold or the time you’re aiming for. Time from my power tells you roughly how long the climb will take at a steady effort. Power for a target time tells you what that goal asks of you; add your FTP to see it as a percentage of FTP and a training zone, so you can judge whether it’s realistic.

Why W/kg decides most climbs

Pedalling power goes into three things: lifting you and the bike against gravity, rolling resistance from the tyres, and pushing air out of the way. On the flat, air resistance takes most of it. On a climb you’re slower and fighting gravity, so the split flips. In the example above, 90% of the power goes into lifting rider and bike, while the same 250 W on flat road would push 85% of it into the air.

That’s why power-to-weight (W/kg) is the number most climbers watch: once gravity dominates, climb time depends mostly on power divided by total mass. Aerodynamics still counts on shallow gradients and fast climbs, which is why the drag area is adjustable under Model assumptions. The power zone calculator shows your W/kg at FTP.

Pacing a climb

On a steady gradient, holding an even power is close to the most efficient way to the top; if the gradient varies, pushing slightly harder on the steep ramps and easing a little on the flatter sections can help. The mistake most riders make is starting too hard: the first minutes feel easy, and the cost arrives later. Pace by power, not speed, because speed swings with every change in gradient.

• Climbs up to about 20 minutes: efforts around threshold (Z4) are common for trained riders.
• Climbs of 30–60 minutes: high tempo to low threshold (upper Z3 to low Z4) is usually more sustainable.
• Longer climbs, or several in a day: tempo and endurance efforts leave something for the rest of the ride.

These are starting points, not rules. Your own zones come from your FTP — see FTP and power zones for how it’s estimated.

What the estimate leaves out

• Wind. A headwind slows you; a tailwind helps. The model assumes still air.
• Gradient changes. An average gradient hides steep ramps and easier sections, so real climbs can take a little longer.
• Altitude. Thinner air reduces drag slightly, but it also reduces the power most riders can sustain.
• Road and tyres. Rough surfaces and heavier tyres raise rolling resistance.
• Riding in a group. Drafting matters less on climbs than on the flat, but it isn’t zero.
• Fatigue and heat. Power you can hold fresh may not be there after three hours in the heat.

Methodology

The calculator uses the standard steady-state model of road cycling power: power at the pedals equals the force of gravity along the slope, plus rolling resistance, plus aerodynamic drag, multiplied by speed and divided by drivetrain efficiency. It solves for the speed a given power produces, or the power a given speed needs. Defaults: CdA 0.40 m², Crr 0.005, air density 1.2 kg/m³ (near sea level), drivetrain efficiency 97.5% and g = 9.81 m/s², with no wind and no acceleration. VAM is metres climbed per hour. W/kg uses your body weight only. Alpe d’Huez uses its commonly quoted 13.8 km at 8.1%.

Sources

• Martin, J. C., Milliken, D. L., Cobb, J. E., McFadden, K. L. and Coggan, A. R. (1998). Validation of a mathematical model for road cycling power. Journal of Applied Biomechanics, 14(3), 276–291.