Beer-Lambert Law Calculator

Concentration is directly proportional to Absorbance in the Beer-Lambert law (c = A / (εl)), so a higher Absorbance reading always produces a proportionally higher calculated Concentration, holding Molar Absorptivity and Path Length fixed. Doubling the Absorbance input exactly doubles the resulting Concentration.

Path Length sits in the denominator of c = A / (εl): for the same measured Absorbance, a longer path length (more solution for light to travel through) means less concentration is needed to produce that absorbance, so the calculator reports a lower Concentration. This is why using a shorter or longer cuvette than assumed changes the result even when the reading itself is identical.

No. % Transmittance is T% = 10^(-A) x 100, a logarithmic (inverse exponential) relationship, not a straight line. Small increases in Absorbance at low values cause large drops in Transmittance, while at high Absorbance, Transmittance approaches zero and further increases in Absorbance barely change it further in absolute terms.

6600 L/(mol·cm) is the standard molar extinction coefficient for double-stranded DNA measured at a wavelength of 260 nm, one of the most common spectrophotometry measurements in molecular biology labs for estimating nucleic acid concentration. Different molecules and wavelengths have very different molar absorptivity values, so this input should always be set to match the actual substance being measured.

The law assumes each absorbing molecule acts independently of the others, which is a good approximation only at low-to-moderate concentration. At high concentration (typically above an absorbance of about 1.0-2.0), solute molecules can interact with each other, and instrument effects like stray light become significant, causing real measured absorbance to deviate from the ideal linear relationship with concentration this calculator assumes.