How this calculator works
Use decadic absorbance and a molar absorption coefficient in L mol^-1 cm^-1. The calculator converts concentration to mol/L and path length to centimetres before multiplying. The law assumes a homogeneous sample, narrow spectral bandwidth and negligible scattering. Concentrated samples, chemical equilibria and stray light can cause deviations.
Formula
A = epsilon c l; A = -log10(T), with T = transmitted/incident radiant power.
Worked example
epsilon = 100 L mol^-1 cm^-1, c = 0.01 mol/L and l = 1 cm give A = 1 and T = 10%. A = 2 gives T = 1%.
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Frequently asked questions
Is absorbance a percentage?
No. Absorbance is a logarithmic ratio. Transmittance can be displayed as a percentage.
Which coefficient convention is used?
The decadic molar coefficient. A coefficient based on natural logarithms differs by ln(10).
Can a blank produce zero absorbance?
Yes. A zero measured absorbance gives full transmittance and a zero inferred concentration in this ideal model.