Objective: The average glandular dose (AGD) is used to evaluate the radiation dosage in mammography. Dance et al. (2000) presented a computation formula to estimate the AGD based on several coefficient factors, such as compressed breast thickness, breast tissue composition, and half-value layers (HVLs). The objective of this study was to improve the preciseness of AGD estimation.Materials and Methods: We interpolated the coefficients developed by Dance et al. to generate an approximation formulae and reference datasets with higher granularity and breast thickness (2–6 cm) relevant to a Japanese population.Results: The results from this study indicate that the incorporation of HVLs and breast thickness required in mammography densitometry leads to an advancement in the current method for estimating the average glandular dose.Conclusions: We expect that these interpolated values will serve as a reference for other researchers and allow for a more accurate, detailed, and individualized AGD estimation.