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Chemistry

Beer–Lambert Law Calculator

Find concentration from absorbance, molar absorptivity and optical path length.

Explicit units and model assumptionsLocal calculations with worked examples
Chemistry workspace
Chemistry workspace

Check the units, concentration basis and assumptions before interpreting the result.

See the method

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Your chemistry result

Your result

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Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter absorbance, molar absorptivity, optical path length.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

A = εlc; concentration c = absorbance ÷ (molar absorptivity × path length). Transmittance = 10^(−A).

A WORKED EXAMPLE

Using absorbance = 0.5, molar absorptivity = 10000 L/(mol·cm), optical path length = 1 cm, the result is 0.00005 mol/L. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

No. Absorbance is logarithmic and dimensionless. For example, absorbance 1 corresponds to 10% transmittance.

What to keep in mind

Assumes the measurement lies in the linear calibration range, with appropriate blank correction and no significant scattering. Educational calculation only; use validated procedures for laboratory work.

Reference: OpenStax Chemistry 2e — chemical quantities and models

Common questions

Is absorbance a percentage?

No. Absorbance is logarithmic and dimensionless. For example, absorbance 1 corresponds to 10% transmittance.

Are my inputs uploaded?

No. This calculation runs in your browser without an account or an external API.

Methodology maintained by ClarityKit. How these tools are built and checked.