It is assumed that the absorbance of each species is proportional to the concentration of that species, according to the Beer–Lambert law.
where λ is a wavelength,  is the optical path length of the cuvette which contains the solution of the N compounds (chromophores),
 is the molar absorbance (also known as the extinction coefficient) of the ith chemical species at the wavelength λ, c is its concentration. When the concentrations have been calculated as above and absorbance has been measured for samples with various concentrations of host and guest, the Beer–Lambert law provides a set of equations, at a given wavelength, that which can be solved by a linear least-squares process for the unknown extinction coefficient values at that wavelength.