In mesoscopic physics, the Landauer formula —named after Rolf Landauer, who first suggested its prototype in 1957 —is a formula relating the electrical resistance of a quantum conductor to the scattering properties of the conductor. It is the equivalent of Ohm's law for mesoscopic circuits with spatial dimensions in the order of or smaller than the phase coherence length of charge carriers (electrons and holes). In metals, the phase coherence length is of the order of the micrometre for temperatures less than 1 K.