Surface roughness is one of the essential characteristics of frictional contact. It controls the most important property, which is the discrete contact of solids and affects the actual contact area, contact pressure, the friction coefficient, roughness determines the surface deterioration mechanism due to friction (wear).

Initial roughness is a result of machine processing of the material surface with abrasives, for example. A great number of surfaces have a horizontal roughness width in the range of 1 to 1000 micrometres, and a height ranging from 0.01 to 10 microns. As a rule, friction and wear change the parameters of initial roughness and cause operational roughness. Operational roughness appearing under steady-state friction conditions is called equilibrium roughness.

Profilometry is used to measure and analyse roughness parameters.

See also subroughness.