🌈 UV Spectroscopy Calculator
Beer-Lambert Law, Molar Absorptivity and Transmittance ↔ Absorbance converter — all in one page.
Beer-Lambert
Solve for any variable — absorbance, concentration, molar absorptivity or path length.
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Type in either field — Transmittance ↔ Absorbance converts as you type.
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Frequently asked questions
Why do I need molar absorptivity to calculate concentration?
Molar absorptivity (ε) is a substance-specific constant that relates absorbance to concentration via the Beer-Lambert Law (A = εcl). Without knowing ε for your specific compound at your measurement wavelength, absorbance alone cannot be converted into a concentration value.
What's the difference between absorbance and transmittance?
Transmittance is the fraction of light that passes through a sample; absorbance is its negative base-10 logarithm. Absorbance is used for quantification because it scales linearly with concentration, while transmittance does not.
What happens if my absorbance reading is outside the linear range?
The Beer-Lambert Law only holds linearly within a limited absorbance range, typically 0.1-1.0 for most instruments. Above roughly 1.5-2.0, deviations from linearity become significant — dilute your sample and re-measure rather than trusting a high-absorbance reading directly.
Accuracy & how this is derived
Derivation: Based on the Beer-Lambert Law (A = εcl), algebraically rearranged to solve for concentration, absorptivity, or path length as needed, with LOD/LOQ calculated using the standard calibration-curve method (3.3σ/S and 10σ/S).
Validated against: Beer-Lambert Law, a foundational law of quantitative spectroscopy, and ICH Q2(R1) for LOD/LOQ methodology.
⚠️ 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
Beer-Lambert law: practical application in analytical labs
Beer-Lambert law (A = εcl) is the foundation of UV-Vis spectrophotometry. To apply it: measure absorbance at the analyte's wavelength maximum, use a 1 cm path length cuvette, and know ε from literature or a calibration curve. Linear range is typically A = 0.05–1.0; above A = 1.0 stray light causes detector non-linearity. For nucleic acids: DNA at 260 nm, ε ≈ 6600 L mol−1 cm−1 per base pair. LOD = 3.3σ/S and LOQ = 10σ/S per ICH Q2(R1), where σ is the residual standard deviation of the regression and S is the slope.