Beer-Lambert Law Calculator
Use this Beer-Lambert law calculator to solve absorbance, concentration, or transmittance for UV-Vis style measurements.
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Run the calculator.
What This Beer-Lambert Law Calculator Helps You Do
Beer-Lambert law is central to spectroscopy because it ties concentration to optical response in a compact equation. This page groups the forward and inverse calculations so you can move between absorbance, concentration, and transmitted light without extra algebra.
That is useful for UV-Vis practice problems, calibration checks, and quick lab estimates where you want to know not just the missing value but also whether the optical signal falls in a sensible range.
How to Calculate Beer-Lambert Law Calculator
- Choose the Beer-Lambert task: Solve for absorbance, concentration, or transmittance.
- Enter optical inputs: Use molar absorptivity in L mol^-1 cm^-1 and path length in cm.
- Calculate the missing value: The tool applies Beer-Lambert law and, when relevant, converts absorbance to transmittance.
- Interpret the optical signal: Higher absorbance means less transmitted light for the same path length.
Beer-Lambert Law Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| A | Absorbance | unitless |
| epsilon | Molar absorptivity | L mol^-1 cm^-1 |
| l | Path length | cm |
| c | Concentration | mol/L |
| T | Transmittance | fraction or percent |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- epsilon: 15000 L mol^-1 cm^-1
- l: 1.0 cm
- c: 2.0 x 10^-5 mol/L
Result: Absorbance is 0.300 and transmittance is 50.12%.
A modest absorbance still blocks about half the incident light.
- A: 0.48
- epsilon: 22000 L mol^-1 cm^-1
- l: 1.5 cm
Result: Concentration is 1.4545 x 10^-5 mol/L.
Rearranging the Beer-Lambert expression isolates concentration directly.
- A: 0.70
Result: Transmittance is 19.95%.
An absorbance of 0.70 leaves only about one fifth of the light transmitted.
- A: 0.15
Result: Transmittance is 70.79%.
Low absorbance values correspond to relatively high transmitted light.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Low absorbance | More light is transmitted through the sample. | Check whether the signal is high enough for reliable measurement. |
| Moderate absorbance | The sample attenuates a noticeable fraction of the beam. | This is often a useful working range for quantitative analysis. |
| High absorbance | Very little light reaches the detector. | Consider dilution or a shorter path length if detector saturation is a concern. |
Frequently Asked Questions
References
Last reviewed: March 2026