# Skin Friction Coefficient

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Skin friction coefficient, abbreviated as $$C_f$$, a dimensionless number, is the ratio of shear stress and dynamic pressure of a free stream.

### Skin Friction Coefficient FORMULA

$$\large{ C_f= \frac{\tau}{ \frac{1}{2} \; \rho \; v^2 } }$$

$$\large{ C_f = \frac{\tau}{q} }$$

Where:

$$\large{ C_f }$$  = skin friction coefficient

$$\large{ \rho }$$  = fluid density

$$\large{ q }$$  = dynamic pressure

$$\large{ \tau }$$ (Greek symbol tau) = fluid shear stress

$$\large{ v }$$  = fluid velocity