ρs is the resistance per unit surface of a sample and is also called sheet resistance. In order to distinguish this from resistance, it is written Ω/□ or Ω/sq.. Since surface resistivity varies with the sample thickness, it is often used to evaluate paint and thin films.
Surface Resistivity ps [ Ω/sq.] = R [ Ω] ∙ RCF = ρv x (1 / t)