Enter your velocity, reference area, fluid density, and drag coefficient (Cd) into this Drag Coefficient Calculator to find the drag force, plus Reynolds number, dynamic pressure, and effective drag area — all switchable between metric and imperial units.
Drag Force
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Reynolds Number
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Dynamic Pressure
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Effective Drag Area
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The drag force equation is Fd = 1/2 × ρ × u² × A × Cd, where Fd is drag force, ρ is fluid density, u is velocity, A is reference area, and Cd is the drag coefficient.
The drag coefficient depends on the object's shape and surface roughness. Common values are: sphere (0.47), long cylinder (1.2), flat disk (1.28), and streamlined bodies (0.04-0.1).
The reference area is the cross-sectional area of the object perpendicular to the direction of motion. For a sphere, it's πr², and for a cylinder, it's the projected area facing the flow.
Drag force increases with the square of velocity. Doubling the speed results in four times the drag force, making high-speed motion increasingly energy-intensive.
The drag coefficient is influenced by object shape, surface roughness, Reynolds number, and flow conditions. Streamlined shapes have lower coefficients than blunt objects.
Terminal velocity occurs when drag force equals gravitational force. Set Fd = mg and solve for velocity: v = √(2mg/(ρACd)), where m is mass and g is gravitational acceleration.
Form drag results from pressure differences around an object's shape, while skin friction comes from fluid viscosity at the surface. The drag coefficient accounts for both effects.