Drag Force Calculator

Frequently Asked Questions

How does speed affect drag force?

Drag grows with the square of velocity, so doubling the speed quadruples the drag force, all else equal. Tripling the speed multiplies it by nine.

What is a typical drag coefficient?

Streamlined airfoil near 0.05, a modern sedan 0.28-0.32, a sphere about 0.47, a skydiver belly-down close to 1.0, and a flat plate facing the flow above 1.2.

What reference area should I use?

For blunt bodies use the projected frontal area facing the flow, in square meters. Published drag coefficients usually assume frontal area, though lift-and-drag tables for wings sometimes use planform area instead, so match the area to the source of your drag coefficient.

What is the difference between drag force and terminal velocity?

Drag force is the instantaneous resistance F = ½ρv²C_dA at any speed. Terminal velocity is the specific steady speed a falling object reaches when that drag force grows to exactly equal its weight, so the net force is zero and it stops accelerating. Set drag equal to mg and solve for v to get it: v = √(2mg / (ρC_dA)). Use the terminal velocity calculator for that fall-speed case.

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How This Calculator Works

The drag equation, F_d = ½ · ρ · v² · C_d · A, gives the aerodynamic or hydrodynamic resistance a body feels as it moves through a fluid. The force grows with the fluid density ρ (kg/m³), the reference area A (m²), the dimensionless drag coefficient C_d of the shape, and most strongly with the square of the speed v (m/s). Because of the v² term, doubling the speed quadruples the drag force and tripling the speed multiplies it by nine. This makes drag the dominant resistance at highway and freeway speeds.

How To Use It

Enter the fluid density in kilograms per cubic meter (1.225 for air at sea level and 20°C, about 1,000 for water). Add the velocity in meters per second, the dimensionless drag coefficient for the shape, and the reference area in square meters, which is usually the projected frontal area facing the flow. The calculator returns the drag force in newtons.

Typical Drag Coefficients

A streamlined airfoil sits near 0.05, a modern sedan around 0.28-0.32, a sphere about 0.47, a cyclist in a tuck near 0.7, a skydiver belly-down close to 1.0, and a flat plate facing the flow above 1.2. The reference area is the projected frontal area in the direction of motion unless a published C_d specifies otherwise (lift-and-drag tables sometimes use wing planform area instead).

Tips

Speed dominates: small velocity changes shift drag sharply.

Air density falls with altitude, reducing drag (a key factor for aircraft and high-altitude skydiving).

Use the projected frontal area for blunt bodies.

For very low Reynolds numbers (very small or slow objects in viscous fluids), Stokes drag F = 6πμrv applies instead of the v² law, where μ is the fluid's dynamic viscosity, r the sphere radius, and v the speed.

Worked Example: Highway Cruising

A car at v = 30 m/s (108 km/h, 67 mph) with C_d = 0.30 and frontal area A = 2.2 m² in air of ρ = 1.225 kg/m³ experiences F_d = 0.5 × 1.225 × 30² × 0.30 × 2.2 ≈ 364 N. Cutting speed to 20 m/s drops drag to about 162 N: less than half, even though speed only fell by a third. This is why fuel economy improves sharply at lower highway speeds. See also the terminal velocity calculator, which uses the same drag equation balanced against gravity.

Drag Force Calculator

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