💡 Beer–Lambert Law Calculator
Relate absorbance to concentration with A = εlc — enter any three of absorbance, molar absorptivity, path length and concentration to get the fourth.
Concentration (c)
0.00005 M
Beer–Lambert law: A = ε·l·c (absorbance = molar absorptivity × path length × concentration). 🔒 Computed in your browser.
How the beer–lambert law calculator works
The Beer–Lambert law is A = ε·l·c, where A is absorbance, ε the molar absorptivity (M⁻¹cm⁻¹), l the path length (cm), and c the concentration (M). Enter any three and the tool solves for the fourth — most often concentration from a measured absorbance.
The workhorse of UV-Vis spectroscopy: with a known ε and a 1 cm cuvette, absorbance is directly proportional to concentration. Linearity holds at low-to-moderate absorbance (roughly A < 1).
Frequently asked questions
What is the Beer–Lambert law?
A = εlc: absorbance equals molar absorptivity times path length times concentration. It says absorbance is proportional to how much light-absorbing substance the beam passes through.
How do I find concentration from absorbance?
Rearrange to c = A / (ε·l). With ε and the cuvette path length (usually 1 cm) known, divide your measured absorbance to get concentration. The tool does this when you solve for c.
What is molar absorptivity (ε)?
A substance-and-wavelength-specific constant (units M⁻¹cm⁻¹) describing how strongly it absorbs light. Higher ε means more absorbance at the same concentration.
What path length should I use?
The width of the cuvette the light passes through — standard cuvettes are 1 cm.
When does the Beer–Lambert law break down?
At high concentration or absorbance (roughly A > 1), where the linear relationship fails due to interactions and stray light. Dilute the sample to stay in the linear range.