CdA calculator
Estimate your CdA (Cd × A) from a ride on flat ground: your power, speed and mass are all you need. To understand what this number represents and compare it with typical values, read our CdA guide.
1. Calculate your CdA
For a reliable estimate, measure on a flat stretch with no wind at a steady speed, and ride out and back to cancel out any residual wind. Don't use the speed shown by your indoor trainer or the average of a whole ride.
2. Analyse your aero efficiency
With your height and your bike, we can estimate your aero efficiency and what you could gain by optimising your aerodynamics on YOUR bike.
Possible gains
Optimised CdA
At the same power
At the same speed
Indicative estimates: do not treat them as exact values.
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These figures are an overall estimate. Your equipment (helmet, wheels, handlebar…) accounts for about 20% of your aerodynamic drag: it can help. But the real lever is your position: your body accounts for about 80% of the drag. The AeroX Diagnostic is designed precisely to optimise the aerodynamics of your position, so you get back the speed you deserve. Discover the Diagnostic →
CdA formula and how to calculate it
The power you produce goes into overcoming three resistances:
On the flat with no wind, the slope term disappears. You can then isolate CdA:
- P
- your power (W)
- η
- drivetrain efficiency ≈ 0.97
- v
- your speed (m/s)
- m
- rider + bike mass (kg)
- ρ
- air density ≈ 1.225 kg/m³
- Crr
- rolling coefficient ≈ 0.005
- g
- gravity = 9.81 m/s²
- θ
- slope angle
See typical CdA values by position →
Measure your frontal area, position by position
The AeroX Diagnostic: up to 10 positions compared live, a hold test on the best one, then your recommended position with your gains in time and km/h. One-off payment.
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