How to use this calculator

Choose a shape to fill in a typical drag coefficient, or type your own C_D. Enter the frontal area (the silhouette seen from the direction of travel), the speed relative to the fluid and the fluid density. To get a terminal velocity, also enter the object’s mass. The graph shows how quickly drag grows with speed.

Formulas

Drag equationF_D = ½ ρ V² C_D A = q C_D A

Power to overcome dragP = F_D V = ½ ρ V³ C_D A

Terminal velocity (drag = weight)V_t = √(2 m gρ C_D A)

Worked example

A sphere with 0.05 m² frontal area at 20 m/s in air (the default)

Dynamic pressure: q = ½ × 1.204 × 20² = 240.8 Pa.
Drag: F_D = 240.8 × 0.47 × 0.05 = 5.66 N.
Power: P = 5.66 × 20 = 113 W.

An 80 kg skydiver, belly to earth (C_D ≈ 1.0, A ≈ 0.7 m²)

V_t = √(2 × 80 × 9.807 / (1.204 × 1.0 × 0.7)) = 43.1 m/s, about 155 km/h (96 mph).

Typical drag coefficients

C_D depends on the shape and, more weakly, on the Reynolds number. Blunt shapes leave a wide turbulent wake and have C_D near 1; streamlined shapes let the flow close smoothly behind them and can reach 0.04. A smooth sphere has C_D ≈ 0.47 over a wide range of speeds, then drops sharply to about 0.1 when the boundary layer turns turbulent (the drag crisis near Re ≈ 3 × 10⁵), which is why golf balls have dimples. Modern cars are around 0.25 to 0.35, pickups and SUVs 0.35 to 0.45, and an upright cyclist about 0.9.

Assumptions and limits

C_D is constant over the speed range. For precise work, take it from wind-tunnel data at your Reynolds number.
Incompressible flow: below about Mach 0.3 (roughly 100 m/s in air). Near the speed of sound drag rises sharply.
For very slow, small objects (Re < 1, such as dust or fine sediment) drag is linear in speed, given by Stokes’ law F = 3πμDV, instead.
Terminal velocity uses standard gravity and ignores buoyancy, which matters only for objects not much denser than the fluid.

Frequently asked questions

Why does highway driving use so much more fuel?

Drag force grows with V², and the power to overcome it with V³. Going from 55 to 75 mph raises aerodynamic power by (75/55)³ ≈ 2.5 times.

What area should I use?

For bluff bodies such as cars, spheres and people, use the frontal (projected) area. Wings and flat plates parallel to the flow are usually quoted with planform area instead, so match the area to how C_D was defined.

Does drag depend on air density at altitude?

Yes, directly. At Denver’s 1,600 m the air is about 17% thinner than at sea level, so drag at the same speed is about 17% lower and terminal velocity about 10% higher.