Aerodynamic Drag (CdA) Calculator

Speed alone can't separate how much of your effort went to fighting air versus rolling resistance — a fast, high-power rider and a fast, low-power rider moving at the same speed could have very different aerodynamics. Power lets the calculator work backward: it computes exactly how much force rolling resistance consumes from your weight and tire coefficient, subtracts that power from your total, and attributes the remainder to aerodynamic drag, which is what CdA actually measures.

Aerodynamic drag force grows with the square of speed, while rolling resistance force stays roughly constant regardless of speed. At low speeds, rolling resistance makes up a much larger share of your total power demand, so a small measurement error in your power or speed data gets amplified into a much larger error in the aerodynamic portion the calculator is trying to isolate. Testing at a sustained, higher speed (30+ km/h) on a calm day gives a more trustworthy CdA estimate.

This calculator assumes zero wind, so any real headwind or tailwind during your test segment directly corrupts the CdA estimate — a headwind makes your CdA look artificially high (it thinks you're pushing extra air resistance when really you're pushing against moving air), and a tailwind makes it look artificially low. For a trustworthy field-test CdA, use a calm day or an indoor velodrome, or do repeated out-and-back runs to average out a steady wind.

A road cyclist in an upright position typically has a CdA around 0.30-0.40 m², a rider in the drops around 0.25-0.32 m², and a dedicated time-trial position with aero equipment can reach 0.19-0.24 m². These are broad, commonly cited ranges rather than fixed targets — actual CdA depends heavily on rider size, position, clothing, and equipment, so use your own calculated value as a baseline to track improvement rather than comparing directly to a stranger's number.