Wien's displacement law states that in a black-body radiation, the wavelength with the maximum intensity is inversely proportional to the temperature of the black body. The wavelength distribution of black body radiation at any temperature has the same "shape" except that each wavelength is displaced on the graph.
wavelengthmax * Temperature = b
In principle, this formula is used to determine the temperature of distant bodies such as stars. In practice, typically more of the spectral energy distribution is evaluated to confirm the determined temperature, and complications such as EMR from different portions (e.g., layers) at different temperatures require accommodation.
Of note is that both the constant and even the location of the peak depend upon the energy density per unit of wavelength of the EMR. An energy density per unit frequency produces a different EMR peak, i.e., a frequencymax that does not directly correspond to the wavelengthmax above. This peak is directly proportional to the black-body temperature, but the constant of proportionality must not only accommodate the Planck constant, but this alternate type of peak.