The molar absorptivity coefficient can be calculated by measuring the absorption of a sample of a known concentration and known pathlength. The absorptivity coefficient units are dependent on the pathlength and concentration units. Molar absorptivity units are L mol-1 cm-1 when the concentration units are molarity. The absorptivity is a measure of how strongly a molecule absorbs light at a particular wavelength. Once this constant is determined, unknown concentrations can be determined from this relationship.