Drag Coefficient Effect Calculator

Work out drag coefficient effect instantly with clear inputs, formula shown and shareable results.

About Drag Coefficient Effect Calculator

Drag power is half rho Cd A v cubed, so it is proportional to Cd. Cutting Cd from 0.32 to 0.28 saves 12.5% of drag power, but the fuel saving is smaller because rolling resistance and driveline losses do not change.

Formula

Drag power

P = 0.5 x rho x Cd x A x v^3; saving is proportional to the change in Cd

Worked example

With the default values below, Drag Coefficient Effect Calculator returns Power saved at cruise of 1.61. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current drag coefficient: 0.32 Cd
Improved drag coefficient: 0.28 Cd
Frontal area: 2.3 m²
Cruising speed: 110 km/h

Results

Power saved at cruise: 1.61 kW
Fuel saving at cruise: 8.81% %
Drag power before: 12.86 kW
Drag power after: 11.25 kW

Step by step

1Values used
2Drag power
3Power saved at cruise= 1.61 kW
4Fuel saving at cruise= 8.81 %
5Drag power before= 12.86 kW
6Drag power after= 11.25 kW

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

At what speed does drag start to dominate?

Around 70-80 km/h for a typical car. Below that rolling resistance dominates and aerodynamic improvements barely register.

What Cd values are typical?

0.30-0.35 for a modern hatchback, 0.24-0.28 for an aerodynamic saloon or EV, and 0.35-0.45 for an SUV or van.