The specific (lat: characteristic) resistance or resistivity is the standardized resistance in ohm of a substance or conductor. Resistivity is the reciprocal of conductivity and indicates the value in ohm of a conductor with a diameter of 1 mm² at a length of 1m. The symbol is ρ (rho), the unit ohm ∙ mm²/m and the value (at least for typical conductor and resistor materials) is indicated in the material data. With this value, it is easy to compute the actual value for a given conductor size.