In fluid dynamics, the pressure coefficient is a dimensionless number which describes the relative pressures throughout a flow field.  The pressure coefficient is used in aerodynamics and hydrodynamics.  Every point in a fluid flow field has its own unique pressure coefficient, .
In many situations in aerodynamics and hydrodynamics, the pressure coefficient at a point near a body is independent of body size.  Consequently, an engineering model can be tested in a wind tunnel or water tunnel, pressure coefficients can be determined at critical locations around the model, and these pressure coefficients can be used with confidence to predict the fluid pressure at those critical locations around a full-size aircraft or boat.