# Beer-Lambert Law

The relationship between absorbance and concentration is linear and is described by Beer-Lambert Law, shown in **Figure 1**.

**Figure 1**: The Beer-Lambert Law where **c** is the molar concentration of the detected substance, **A** is the absorbance value returned by the spectrophotometer in arbitrary units (AU), **ε** **L** is the pathlength in cm.

Note, the molar extinction coefficient is also called molar absorptivity. Also, for most spectrophotometers that use standard cuvettes, the path length is 1 cm.

This Beer-Lambert equation is easily rearranged to suit the needs of experimentation. For example, to convert absorbance values into concentration, the equation:

Can be rearranged to: