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. Air density is the standard sea-level value; the rolling resistance, drag area and drivetrain defaults are assumed typical figures for a road rider, not measurements, so 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 in still air needs about 152 watts with the default settings (75 kg rider, 8 kg bike, CdA 0.32 m², Crr 0.005, 97% drivetrain efficiency).
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?
Standard sea-level air density (1.225 kg/m³) plus assumed typical values for a road rider: drag area (CdA) 0.32 m², rolling resistance (Crr) 0.005 and ~97% drivetrain efficiency. Those three are not measured for you, so adjust them for your bike and position.
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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