How to find concentration from absorbance

The Beer-Lambert law says absorbance is directly proportional to concentration: A = εbc. Here A is the measured absorbance, ε (epsilon) is the molar absorptivity — a constant for a given substance and wavelength — b is the path length of the cuvette (almost always 1 cm), and c is the molar concentration. To find an unknown concentration, rearrange to c = A / (εb). If your instrument reports %transmittance instead of absorbance, convert first with A = −log₁₀(T), where T is the fraction of light transmitted (%T divided by 100). The law holds best at low absorbance (roughly A < 1); above that, readings deviate from linearity.

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