Enter the molar absorption coefficient, concentration, and path length into the calculator to determine the total absorbance.

Beer-Lambert Law Formula

The following equation is used to calculate the absorbance of a substance.

A = ma * c * l 
  • Where A is the absorbance
  • ma is the molar absorption coefficient (m*2/mol)
  • c is the concentration (mol/L)
  • l is the path length (m)

To calculate absorbance from the Beer-Lambert Law, multiply the molar absorption coefficient by the concentration, then multiply by the path length.

Beer-Lambert Law Definition

The Beer-Lambert Law, also known as the Beer-Lambert-Bouguer Law or simply Beer’s Law, is a fundamental principle in spectroscopy that relates the concentration of a solute in a solution to the absorption of light by that solution.

It is named after the scientists August Beer and Johann Lambert, who independently formulated the law in the mid-19th century.

The law states that the absorbance (A) of light passing through a sample is directly proportional to the concentration (c) of the absorbing species and the path length (l) that the light travels through the sample. Mathematically, this relationship is represented as A = εcl, where ε is the molar absorptivity or molar absorption coefficient, a constant unique to each absorbing species and wavelength of light.

The Beer-Lambert Law is crucial in various scientific disciplines, particularly chemistry, biochemistry, and environmental science. It provides a quantitative method to determine the concentration of a solute in a solution by measuring the absorbance of light at a specific wavelength.

This enables scientists to analyze the composition and concentration of substances, such as pollutants in water, reactants in chemical reactions, or biomolecules in biological samples.

Beer-Lambert Law Example

How to calculate absorption from the Beer-Lambert law?

  1. First, determine the coefficient.

    Calculate the molar absorption coefficient of the substance.

  2. Next, determine the concentration.

    Calculate the concentration of the substance.

  3. Next, determine the path length.

    Calculate the length of the path in which the substance can be absorbed.

  4. Finally, calculate the absorption.

    Calculate the absorption using the formula above.


What is the Beer Lambert Law?

This law states that the absorbance is proportional to the length and the concentration of a material.