You can calculate in the below Absorbance to Milli Absorbance conversion formula to convert the value in Absorbance (Abs) to Milli Absorbance (mAbs). As milli absorbance is one-thousandth of absorbance, mAbs is calculated as mAbs = Abs / 1000. Absorbance is defined as a measure of the capacity of a substance to absorb light of a specified wavelength. It is equal to the logarithm of the reciprocal of the transmittance. Hope this page is helpful for your learning.