Cycling Power Calculator
Estimate the power (watts) needed to ride at a given speed and gradient from rolling resistance, air drag, and gravity — a physics-based model. Runs in your browser.
Power required
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Show the math
Power overcomes three resisting forces, then accounts for drivetrain loss:
P = (rolling + gravity + air) × speed ÷ 0.97
Air drag grows with the square of speed, so it dominates on the flat; on a climb, gravity takes over. The model assumes still air, riding into a headwind needs more power than shown. Defaults suit a road rider; tune Crr and CdA for your setup.
What this does
A cycling power calculator estimates the power in watts needed to ride at a given speed and gradient, combining rolling resistance, air drag, and gravity in a physics-based model.
How it works
It sums the three forces a rider overcomes (rolling resistance, aerodynamic drag, and gravity on a slope) multiplies by speed, then divides by drivetrain efficiency to get the power at the pedals.
How to use it
- Enter your speed and the gradient.
- Enter rider and bike weight.
- Adjust drag (CdA) and rolling resistance if known.
- Read the estimated power in watts.
Understanding your result
The model uses still-air drag with sensible defaults for a road rider. A headwind raises your speed through the air, so real power into a wind will be higher than shown.
Example
Holding 30 km/h on flat ground typically needs around 200 watts for a road cyclist.
Sources & methodology
Last updated .
Frequently asked questions
How is power estimated?
It sums the three forces a rider overcomes — rolling resistance, aerodynamic drag, and gravity on a slope — multiplies by speed, then divides by drivetrain efficiency to get the power at the pedals.
What assumptions does it make?
Sensible defaults for drag area (CdA), rolling resistance (Crr), air density, and ~97% drivetrain efficiency. These suit a road rider; adjust the inputs for your setup.
Why does wind not appear?
The model uses still-air drag. A headwind effectively raises your speed through the air, so real power into a wind will be higher than shown.
Do you keep my numbers?
No. All calculations happen locally in your browser.
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