Beer–Lambert Law Calculator
Enter the molar absorptivity ε, path length b, and concentration c to compute absorbance via the Beer–Lambert law A = ε·b·c.
Input Data
Results
At a glance:Enter the molar absorptivity ε, path length b, and concentration c to compute absorbance via the Beer–Lambert law A = ε·b·c.
Formula
A = ε · b · c.
$$A = \varepsilon \cdot b \cdot c$$How to Use
- Enter the molar absorptivity ε (L·mol⁻¹·cm⁻¹).
- Enter the path length b (cm) and concentration c (mol/L).
- The calculator returns the absorbance A.
FAQ
What is the Beer–Lambert law?
It states that a solution's absorbance is proportional to the molar absorptivity, path length, and concentration: A = ε·b·c. Because absorbance is proportional to concentration, it can be used to quantify solution concentration.
Why does absorbance have no unit?
Absorbance is defined as the logarithm of the ratio of incident to transmitted light intensity, A = log₁₀(I₀/I), which is the log of a ratio of two intensities and therefore a dimensionless pure number.
How do I get concentration from absorbance?
Rearrange A = ε·b·c to c = A/(ε·b). In practice, first build a standard curve of absorbance vs concentration using known standards, then read the sample's concentration from its absorbance.
Why is high absorbance inaccurate?
The Beer–Lambert law is most accurate for dilute solutions and low absorbance. At high concentration (generally A>1), intermolecular interactions and refractive-index changes break the linearity, so high-concentration samples should be diluted first.
What is the molar absorptivity ε?
ε is an intrinsic property of a substance describing its light-absorbing ability at a given wavelength, in L·mol⁻¹·cm⁻¹; a larger value means stronger absorption. It varies with wavelength, so measurements usually use the wavelength of maximum absorption, λmax.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.