Drag Coefficient

A dimensionless value that allows the comparison of shape and orientation of different bodies.

Circular flat plate	Cd = 1.12 Re ~ 1e6 A = πd2/4
Sphere	Cd = 0.45 Re < 2e5 A = πd2/4 Cd = 0.2 Re > 2e5 A = πd2/4
Solid Hemisphere	Cd = 0.38 Re = 1e3 A = πd2/4
Solid Hemisphere	Cd = 1.17 Re = 1e3 A = πd2/4

Miscellaneous Objects

Cd	Object
1.0 to 1.4	skydiver
1.0 to 1.3	person standing
0.9	bicycle
0.7 to 1.1	formula one race car
0.6	bicycle with faring
0.35 to 0.45	light truck
0.25 to 0.35	car
0.05	airfoil
0.15	airfoil at stall

See also: Drag, Pressure Coefficient, Vehicle Aerodynamic Drag.

Further reading:
• Competition Car Aerodynamics: A Practical Handbook, Simon McBeath, Haynes Group

Weblinks:

Aerospaceweb.org - Golf Ball Dimples The aerodynamics of spheres and spheres with dimples - more commonly known as golf balls.