Absorbance is a dimensionless unit, which is also called as Decadic Absorbance. It is defined and expressed as the common logarithm of the ratio of incident to transmitted radiant power into a material. It is the measure of the capacity of a substance to observe the radiation. It is referred as optical density, as it is an induction of how much a material can stop the light. You can convert transmittance to absorbance using this online calculator.
If the transmittance of a material is 23, calculate absorbance?
Absorbance = -Log10(T)
= - log10 (23)