How this calculator works
Drag opposes motion relative to a fluid. The quadratic relation combines dynamic pressure with a dimensionless coefficient and a chosen reference area. Match the area definition to the coefficient source, often frontal area for a bluff body. The coefficient can change with Reynolds number, Mach number and orientation; it is held fixed in reverse modes.
Formula
D = Cd rho v^2 A/2. Dynamic pressure q = rho v^2/2; D = Cd q A.
Worked example
For rho = 1.2 kg/m3, v = 10 m/s, Cd = 0.8 and A = 2 m2, drag is 96 N. At 20 m/s with the same coefficient it is 384 N.
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Frequently asked questions
What speed belongs here?
Use speed relative to the surrounding fluid, including wind or current.
Can I use wing area?
Yes if the published drag coefficient uses wing area. Mixing reference-area conventions gives an incorrect force.
Does the force include its direction?
This page returns a magnitude. Drag acts opposite the relative motion.