Aerodynamic Drag Power Calculator

Aerodynamic drag is the resistance of the air a vehicle pushes through. The drag force equals one half times the air density times the drag coefficient times the frontal area times the speed squared. Because drag force rises with the square of speed, the power needed to overcome it rises with the cube of speed, which is why high-speed cruising is so demanding on energy.

Drag force F equals 0.5 times rho times Cd times A times v squared, where rho is air density, Cd is the drag coefficient, A is the frontal area, and v is speed in metres per second. The power to overcome it is the force times speed, which equals 0.5 times rho times Cd times A times v cubed.

Standard sea-level air density is about 1.225 kilograms per cubic metre at 15 degrees Celsius. Density falls with altitude and rising temperature, which reduces drag at elevation. Because it varies with conditions, this calculator takes air density as a user-editable input so you can match your altitude and temperature.

Modern passenger cars often have drag coefficients in the rough range of 0.25 to 0.35 and frontal areas around 2 to 2.5 square metres, while larger or boxier vehicles are higher. These vary by model, so this calculator takes both Cd and frontal area as inputs; use the figures published for your vehicle for an accurate result.

Drag force scales with speed squared, and power is force times speed, so drag power scales with speed cubed. Doubling speed multiplies drag power by eight. This cubic relationship is why fuel use and required power climb steeply at highway speeds and why aerodynamics dominate the road load at higher speeds.