Cycling Power Calculator
The power it takes to ride at a given speed — on the flat or a gradient — from rider and bike weight, aerodynamic drag, rolling resistance and drivetrain losses, with the share each one takes.
Three forces resist a cyclist: rolling resistance (a small constant share of weight), gravity on a climb (weight × gradient), and aerodynamic drag, which grows with the square of speed and dominates above about 25 km/h on the flat.
How the cycling power calculator works
Three forces resist a cyclist: rolling resistance (a small constant share of weight), gravity on a climb (weight × gradient), and aerodynamic drag, which grows with the square of speed and dominates above about 25 km/h on the flat. Power is the total force times speed, divided by drivetrain efficiency. A CdA of 0.32 m² is a rider on the hoods; 0.25 in the drops or on aero bars; Crr 0.005 is a good road tyre on smooth tarmac.
Formula: P = (Crr·m·g·cos θ + m·g·sin θ + ½·ρ·CdA·v²) × v ÷ η
Worked examples
| Inputs | Power required | Note |
|---|---|---|
| 30 km/h on the flat, 75 kg rider | 152 W | about 153 W |
| 15 km/h up a 7% climb | 279 W | about 270 W |
| 40 km/h on aero bars | 264 W | about 245 W |
FAQFrequently asked questions
Why does speed cost so much more on the flat than I expect?
Aerodynamic drag grows with the square of speed, so the power to overcome it grows with the cube: 40 km/h needs about 2.4 times the power of 30. It is why drafting and aero position matter so much.
What CdA should I use?
About 0.40 m² sitting upright, 0.32 on the hoods, 0.28 in the drops, 0.22–0.25 on aero bars in a good position. Loose clothing adds a lot; a skinsuit and aero helmet take it off.
How accurate is this against a power meter?
Within about 10% on a still day if the CdA and Crr are right. Wind is the big unknown — a 10 km/h headwind at 30 km/h raises aero power by about 75%.
What is a good W/kg?
For an hour: around 2 W/kg for a recreational rider, 3 for a fit club cyclist, 4 for a strong racer, 5.5–6 for professionals. On long climbs it is what decides who arrives first.
Where these figures come from
- Riegel PS, "Athletic records and human endurance", American Scientist 1981 — T2 = T1 × (D2 ÷ D1)^1.06
- Cooper KH, "A means of assessing maximal oxygen intake", JAMA 1968 — the 12-minute run test
- Ainsworth BE et al., Compendium of Physical Activities (2024 update) — MET values by activity
- OpenPowerlifting — DOTS coefficients (Tim Konertz, 2019) — the DOTS polynomial used for scoring
- Naismith's rule (1892) as used by UK and Australian walking bodies — 1 hour per 5 km plus 1 hour per 600 m of ascent
- UK Sport — national high-performance body
Last checked: September 2026. Formulas are fixed by their published sources; the MET values come from the Compendium of Physical Activities.