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Purpose: Measurements of breast arterial calcifications (BAC) can offer a personalized, non‐invasive approach to risk‐stratify women for cardiovascular diseases such as heart attack and stroke. We aim to detect and segment breast arterial calcifications in mammograms accurately and suggest novel measurements to quantify detected BAC for future clinical applications. Methods: To separate BAC in mammograms, we propose a lightweight fine vessel segmentation method Simple Context U‐Net (SCU‐Net). Due to the large image size of mammograms, we adopt a patch‐based way to train SCU‐Net and obtain the final whole‐image‐size results by stitching patchwise results together. To further quantify calcifications, we test five quantitative metrics to inspect the progression of BAC for subjects: sum of mask probability metric (PM), sum of mask area metric (AM), sum of mask intensity metric (SIM), sum of mask area with threshold intensity metric TAMX, and sum of mask intensity with threshold X metric TSIMX. Finally, we demonstrate the ability of the metrics to longitudinally measure calcifications in a group of 26 subjects and evaluate our quantification metrics compared with calcified voxels and calcium mass on breast CT for 10 subjects. Results: Our segmentation results are compared with state‐of‐the‐art network architectures based on recall, precision, accuracy, F1 score/Dice score, and Jaccard index evaluation metrics and achieve corresponding values of 0.789, 0.708, 0.997, 0.729, and 0.581 for whole‐image‐size results. The quantification results all show >95% correlation between quantification measures on predicted masks of SCU‐Net as compared to the groundtruth and measurement of calcification on breast CT. For the calcification quantification measurement, our calcification volume (voxels) results yield R2‐correlation values of 0.834, 0.843, 0.832, 0.798, and 0.800 for the PM,AM,SIM,TAM100,TSIM100 metrics, respectively; our calcium mass results yield comparable R2‐correlation values of 0.866, 0.873, 0.840, 0.774, and 0.798 for the same metrics. Conclusions: Simple Context U‐Net is a simple method to accurately segment arterial calcification retrospectively on routine mammograms. Quantification of the calcifications based on this segmentation in the retrospective cohort study has sufficient sensitivity to detect the normal progression over time and should be useful for future research and clinical applications. [ABSTRACT FROM AUTHOR]