AAT Bioquest

How is absorbance calculated from transmittance?

Posted December 15, 2022


To calculate absorbance from transmittance, the Beer Lambert Law for transmittance equation is used: Absorbance= 2 - log (%T). As an example, if a transmittance is calculated to be 45%, absorbance would be calculated as 2-(log)(45)=0.347 AU. As absorbance of light increases, transmittance decreases.

Additional resources

The Bouguer‐Beer‐Lambert Law: Shining Light on the Obscure

Beer Lambert Law Calculator

Absorption Spectrum Viewer