Beer-Lambert Law Calculator (Absorbance and Concentration)
Solve for concentration from absorbance, or absorbance from concentration, for spectrophotometry.
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Beer-Lambert Law Calculator (Absorbance and Concentration) by TheCalcTools
How the Beer-Lambert Law Calculator (Absorbance and Concentration) works
The Beer-Lambert law says absorbance is proportional to concentration and path length: A = εlc. Measure absorbance in a spectrophotometer and divide by εl to get concentration.
Absorbance and transmittance are related by A = −log₁₀ T. The law is most reliable for absorbances between about 0.1 and 1.
The formula
Worked example
Using the default values shown in the calculator:
| Solve for | Concentration |
|---|---|
| Absorbance A | 0.45 |
| Molar absorptivity ε (L/(mol·cm)) | 6220 |
| Path length (cm) | 1 |
| Concentration (mol/L) | 0.0001 |
- c = 0.45 ÷ (6220 × 1) = c = 0.00007235 mol/L.
- Transmittance = 35.5%.
Result:
| Answer | c = 0.00007235 mol/L |
|---|---|
| Transmittance | 35.48% |
| Concentration (µmol/L) | 72.347 |
Frequently asked questions
Why is NADH's ε 6220?
NADH absorbs at 340 nm with a molar absorptivity of about 6,220 L/(mol·cm), widely used in enzyme assays. Use the value for your own compound and wavelength.
Sources and further reading
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