What is the Beer-Lambert law?

Beer-Lambert law states that absorbance (A) equals the product of molar absorptivity (ε, L·mol⁻¹·cm⁻¹), path length (l, cm), and concentration (c, mol/L): A = ε × l × c. It describes how light is attenuated by a solution.

What are the units for each variable?

Absorbance (A) is dimensionless. Molar absorptivity (ε) is in L·mol⁻¹·cm⁻¹. Path length (l) is in centimeters (cm). Concentration (c) is in mol/L (M). Use consistent units for accurate results.

What is the standard cuvette path length?

The standard laboratory cuvette has a path length of 1.0 cm. If you are unsure of your cuvette path length, entering 1 cm is a safe default for most benchtop spectrophotometers.

Does Beer-Lambert law always hold?

The law is accurate at low to moderate absorbances (typically A < 1.0). At high concentrations, stray light, molecular interactions, and detector saturation cause deviations. Dilute samples to stay in the linear range.

What is the molar absorptivity of DNA at 260 nm?

Double-stranded DNA has a molar absorptivity of approximately 6,600 L·mol⁻¹·cm⁻¹ per base pair at 260 nm. A 50 µg/mL solution of double-stranded DNA gives an A260 of about 1.0.

Spectrophotometry Calculator

Name: Spectrophotometry Calculator
Availability: InStock
Author: Nham Vu

Solve Beer-Lambert law (A = εlc) for concentration, absorbance, molar absorptivity, or path length — instantly, client-side.

Beer-Lambert Law: A = ε × l × c

Select what to solve for, then fill in the other three values.

Solve for

Absorbance (A) — dimensionless

Molar Absorptivity (ε) — L·mol⁻¹·cm⁻¹

Path Length (l) — cm

Concentration (c) — mol/L (M)

Result

Enter values and click Calculate.

Concentration

Equation used

Variable	Value	Unit

Common Molar Absorptivity Values

Substance	Wavelength	ε (L·mol⁻¹·cm⁻¹)
NADH	340 nm	6,220
Tryptophan	280 nm	5,500
Tyrosine	280 nm	1,490
HRP	403 nm	150,000
p-Nitrophenol	405 nm	16,500

Click a row to pre-fill ε.

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Summary

Solve Beer-Lambert law (A = εlc) for concentration, absorbance, molar absorptivity, or path length — instantly, client-side.

How it works

Select which variable you want to solve for (concentration, absorbance, molar absorptivity, or path length).
Enter the three known values in their respective fields.
The calculator applies the Beer-Lambert law: A = ε × l × c.
The result is displayed instantly with unit annotations.
Switch the solve-for target at any time to explore different scenarios.

Use cases

Determine protein concentration from UV-Vis absorbance at 280 nm.
Find DNA or RNA concentration from A260 readings.
Verify molar absorptivity of a synthesized compound.
Calculate the expected absorbance for a known concentration standard.
Convert optical density measurements to cell concentration estimates.
Quality-check cuvette path length calibration in spectroscopy labs.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu