Cycling Power Calculator
Works out the steady power a ride takes at a given speed, and where it goes.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
gravity = m × g × sin θ × v rolling = m × g × cos θ × Crr × v drag = ½ × ρ × CdA × (v + wind)² × v power = (gravity + rolling + drag) ÷ (1 − loss)
Here m is the total weight, g is 9.80665 m/s², θ is the slope angle and v is your speed in m/s. Drag rises with the square of the air speed, so its power rises with the cube of your speed.
What to watch out for
This is a simplified form of the road cycling model tested by Martin and colleagues (1998). It leaves out wheel bearing friction and changes in speed. Your position and tyres change the result most, and the drag area and rolling figures here are typical values, not measurements of you.
Power to weight uses rider weight alone, which is how climbers usually quote it.
Frequently Asked Questions
How many watts is 30 km/h on the flat?
About 145 W for an 84 kg rider and bike on the hoods, of which 113 W is air drag.
How much harder is 40 km/h?
About 315 W for the same rider, because drag grows so quickly with speed.
How much does a climb add?
At 15 km/h on a 5% slope the same rider needs about 205 W, with 171 W of it going to gravity.