🔬 Beer–Lambert Law Calculator
Solve for absorbance, concentration, molar absorptivity, or path length using A = ε × c × l.
Frequently asked questions
What is molar absorptivity (ε)?
Molar absorptivity, also called the molar extinction coefficient, is a substance-specific constant describing how strongly it absorbs light at a given wavelength. It's usually reported at a wavelength of maximum absorbance (e.g. ε280 for proteins) and is looked up from literature or determined experimentally from a calibration curve.
Why does Beer-Lambert Law break down at high absorbance?
At high concentrations, effects such as stray light, deviations in the refractive index, and molecular interactions (like aggregation) cause absorbance to no longer scale linearly with concentration. Most instruments are reliable only in the A = 0.1-1.0 range; dilute samples reading above roughly A = 1.5-2.
Can I use this for a mixture of absorbing species?
This calculator assumes a single absorbing species with a known molar absorptivity. For mixtures, you need either a wavelength where only one component absorbs, or a multi-wavelength/multivariate approach outside the scope of this simple calculator.
Accuracy & how this is derived
Derivation: Direct application of the Beer-Lambert Law (A = epsilon * c * l), algebraically rearranged to solve for whichever variable is unknown.
Validated against: Foundational law of quantitative spectroscopy (Beer, 1852; Lambert, 1760), used across all UV-Vis analytical chemistry references.
⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.
✔ Last updated: July 2026 · Report an error
The Beer-Lambert Law in UV-Vis spectroscopy
The Beer-Lambert Law relates the absorbance of a sample to the concentration of the absorbing species, its molar absorptivity at the measurement wavelength, and the optical path length through the sample. It underlies virtually all UV-Vis quantification, from nucleic acid and protein concentration measurements to enzyme assays, and its linear range is the basis for calibration-curve based quantification methods used throughout analytical chemistry and biochemistry.