The resistance of a unit square of a thin-film material, such as a metal or thin layer of semiconductor, defined as R_s = ρ/t where R_s is the sheet resistance, ρ the resistivity, and t the thickness. A film of length L, width W, and thickness t therefore has a total resistance equal to R_s(L/W). R_s has dimensions of resistance but is commonly given the unit ‘ohms per square’.

Single-phase shell-type transformer