One of the most essential parameters in determining deformation of the friction surface is the height of surface roughness. This article studies and compares three different formulas for determination of the mathematical expectation value of surface peak height for the roughnesses being above the determined deformation level γ. The article treats the P.R. Nayak formula and two most well-known probability distribution laws: the normal distribution (Gauss) law and Rayleigh law. The work clearly shows and demonstrates graphically the ME values of surface peak height at different γ values, for all three formulas.