Beer-Lambert Law Calculator

Solve concentration or absorbance using molar absorptivity, path length, and Beer-Lambert law relationships.

Quick Facts

Core Formula
A = epsilon * l * c
Use this as a planning and validation aid, then confirm assumptions for your domain.

Your Results

Calculated
Absorbance A
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Primary output
Transmittance %
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Secondary output
Suggested Range Flag
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Verification metric
Concentration from A=1
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Interpretation

Ready

Enter values and calculate to get scenario outputs.

About the Beer-Lambert Law Calculator - Absorbance and Concentration

Beer-Lambert Law:

A = ε × l × c

A = absorbance; ε = molar absorptivity; l = path length; c = concentration

Concentration calculations are foundational in analytical and preparative chemistry. Whether you're making a solution from scratch, diluting a stock, or measuring absorbance, precise concentration arithmetic is essential.

Key concentration units

  • Molarity (M = mol/L): most common in aqueous chemistry. Temperature-dependent (volume changes with T).
  • Molality (m = mol/kg solvent): temperature-independent. Preferred for colligative property calculations.
  • Mass fraction (w/w %): mass of solute / total solution mass × 100. Unambiguous and temperature-independent.

Dilution formula

C₁V₁ = C₂V₂. The product of initial concentration and volume equals the product of final concentration and volume. Use this to calculate how much stock solution to dilute to reach a target concentration.

Beer-Lambert Law

A = εlc. Absorbance equals the product of molar absorptivity (ε, L/mol·cm), path length (l, cm), and concentration (c, mol/L). This allows concentration determination from a simple spectrophotometric measurement — provided the solution is within the linear range (A typically 0.1–1.0).

Frequently Asked Questions

How accurate are the results?
The Beer-Lambert Law applies a standard formula to your inputs — accuracy depends on how precisely you measure those inputs. For planning and estimation, results are reliable. For high-stakes or professional decisions, cross-check the output with a domain expert or primary source.
What if my reagents aren't 100% pure?
Account for purity in your mass calculation: actual mass needed = theoretical mass / (purity fraction). For example, 95% pure NaCl: if you need 10g of pure NaCl, weigh out 10/0.95 = 10.53g. Always check the Certificate of Analysis for the actual purity of each lot.