Beer-Lambert Concentration Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026The formula behind every spectrophotometer reading
The Beer-Lambert Law relates how much light a solution absorbs to the concentration of the absorbing substance inside it - the fundamental principle behind spectrophotometry, used constantly in biology labs to measure DNA, RNA, and protein concentrations.
Worked example
For an absorbance reading of 0.5, with a molar absorptivity of 5,000 M-1cm-1 and a 1cm path length:
c = 0.5 / (5000 x 1) = 0.0001 M
Frequently asked questions
What is molar absorptivity? It's a constant specific to the particular substance and wavelength being measured, describing how strongly that substance absorbs light at that wavelength - it must be known or looked up for the specific compound before this calculation can be performed.
Why is 1cm path length so common in labs? Standard laboratory cuvettes are manufactured to a standardized 1cm path length specifically so that absorbance readings can be compared directly and consistently across different instruments and experiments.