# drag coefficient

Drag coefficients of various bodies. Credit: NASA.

The drag coefficient is a dimensionless number used in aerodynamics to describe the drag of a shape. The drag coefficient, *C _{d}*, is independent of
the size of the object and is usually determined in a wind
tunnel. It is part of the basic drag equation:

*F* = 0.5 × *ρ* × *V*^{ 2} × *C _{d}* ×

*A*

where *F* is the drag force, *ρ* (rho) is the air density,* V* is the air velocity, and *A* is the cross sectional area. All
of these, except *C _{d}*, are directly measurable in a wind
tunnel so

*C*can be thought of the "fudge factor" that accounts for all of the aerodynamic peculiarities of a shape.

_{d}