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CdA Calculator — Estimate Drag Coefficient Area
Estimate your drag coefficient area from field test data.
How We Calculate This
CdA Estimation
This rearranges the Martin et al. (1998) road-cycling power model. A power meter reads power at the pedals, so we first remove the drivetrain loss (≈2.4%, i.e. 97.6% efficiency) to get power delivered to the road, then strip out the rolling and gravity terms — whatever is left is spent on aerodynamic drag:
- P_road = P_pedal × 0.976
- P_aero = P_road − P_rolling − P_gravity
- CdA = 2 × P_aero / (air_density × v³)
This assumes steady-state conditions — flat, windless laps with accurate power and speed data. Average several runs to cancel residual wind.
Frequently Asked Questions
CdA is the product of the drag coefficient (Cd) and frontal area (A). It represents your total aerodynamic drag profile and is measured in m². Lower is more aerodynamic.
Use a flat, windless course. Record power and speed with a power meter and GPS. Average over multiple laps to reduce wind effects. This calculator then estimates CdA from those averages.
Hoods position: 0.35-0.40 m². Drops: 0.30-0.35 m². TT position: 0.22-0.28 m². Professional TT riders: 0.20-0.22 m².
Aero power scales with CdA: ΔP = ½ × ρ × ΔCdA × v³. At 40 km/h (11.11 m/s) in still air, reducing CdA by 0.01 m² saves about 8 W at constant speed — or, holding power constant, gains roughly 0.4-0.5 km/h. Because power rises with the cube of speed, the saving grows quickly at higher speeds: the same 0.01 m² is worth around 13 W at 47 km/h.
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Last updated: February 2026
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.