Absorbance of a material is also related to its decadic attenuation coefficient by
where
*  is the thickness of that material through which the light travels, and
*  is the decadic attenuation coefficient of that material at .
If a(z) is uniform along the path, the attenuation is said to be a linear attenuation, and the relation becomes
Sometimes the relation is given using the molar attenuation coefficient of the material, that is its attenuation coefficient divided by its molar concentration:
where
*  is the molar attenuation coefficient of that material, and
*  is the molar concentration of that material at .
If  is uniform along the path, the relation becomes
The use of the term "molar absorptivity" for molar attenuation coefficient is discouraged.