How is cycling power estimated?

It adds three forces at the wheel — rolling resistance (Crr × mass × g × cos(slope) × v), aerodynamic drag (0.5 × air density × CdA × v³) and gravity on a slope (mass × g × sin(slope) × v) — then divides by a 0.97 drivetrain efficiency to get rider power.

How accurate is this estimate?

It uses typical defaults (CdA 0.32 m², Crr 0.005, air density 1.225 kg/m³), so it is a ballpark figure for planning, not a substitute for a real power meter. Your true CdA and Crr vary with position, tyres and surface.

Is any data uploaded?

No — the whole calculation runs locally in your browser.

Cycling Power Estimator

Cycling power estimator

Riding at a given speed takes power to overcome three forces: rolling resistance, aerodynamic drag, and gravity on a climb. This estimator combines all three using the standard cycling physics model and divides by drivetrain efficiency to give the watts at the pedals.

Enter your rider + bike mass, target speed, and the road gradient. The result includes watts, watts per kilogram, and a breakdown of where the power goes — all computed in your browser.