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.

How do I get accurate CdA data?

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.

What CdA values are typical?

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.

How much speed does a lower CdA give?

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.

BikeCalcs

CdA Calculator — Estimate Drag Coefficient Area

Estimate your drag coefficient area from field test data.

Average Power

Average pedal power from your power meter over the test

Average Speed

Average ground speed over the test laps

Total Weight (rider + bike)

Rider + bike + kit, in kg

Crr

Road tyre ~0.005

Gradient

Use 0 for flat course

Air Density

Sea level ~1.225; lower at altitude or in heat

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

Related Calculators

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Power to Speed Calculator

Estimate cycling speed from power output accounting for all resistances.

Climbing Power Calculator

Calculate the power needed to climb at a given speed and gradient.

Drag Calculator

Calculate aerodynamic drag force at different speeds.

Wind Resistance Calculator

Calculate the effect of headwind and tailwind on power requirements.

Last updated: February 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.