Beer-Lambert Law Calculator
Calculate any variable in the Beer-Lambert law equation: A = εbc. Solve for absorbance, concentration, molar absorptivity (extinction coefficient), or path length. Also computes percent transmittance.
The Beer-Lambert law (also called Beer's law) is the fundamental equation of UV-Vis spectrophotometry. It relates the absorbance of a sample to the concentration of the absorbing species, the path length of light through the sample, and the molar absorptivity of the species.
The Law: A = εbc
- A = absorbance (dimensionless, also called optical density)
- ε = molar absorptivity (extinction coefficient) in L/(mol·cm)
- b = path length in cm (typically 1 cm for standard cuvettes)
- c = concentration in mol/L
Transmittance Relationship:
Absorbance and transmittance are related by: A = -log₁₀(T) = -log₁₀(I/I₀), where T is the fraction of light transmitted and I/I₀ is the ratio of transmitted to incident light intensity. Percent transmittance = T × 100 = 10^(-A) × 100.
Limitations:
Beer's law is linear only at low to moderate concentrations (typically A < 2). At high concentrations, molecular interactions, scattering, and detector limitations cause deviations from linearity. Always verify linearity with a calibration curve.