Abstract Background: Accurate preoperative assessment of tumor size in relation to that of the breast is an important part of clinical cancer staging that helps in treatment planning. Sonomammography offers adequate accuracy in estimating the tumor-to-breast volume ratio and hence helps in guiding the proper surgical decision. Aim of Study: This study was designed to evaluate the accuracy of the preoperative radiological assessment of tumor size & the tumor-to-breast volume ratio, to guide the appro-priate surgical decision. Patients and Methods: The study was conducted from October 2019 to August 2020. A total of 40 cases diagnosed as having breast cancer using core-needle biopsy after son-omammography were included in the study. On mammography, the maximum tumor dimensions and the breast volume were calculated. On mammography and ultrasound, three measure-ments of the tumor were obtained, from which the tumor volume was measured. Tumor to breast volume ratio was then calculated. The measurements were compared to the postsur-gical pathology reports, which were the gold standard. Results: A total of 40 patients were included in the study. No significant difference was found when comparing the mean of maximum tumor dimension measured on the final pathology (3.240±0.239) to that measured on preoperative ultrasound (3.057±0.237, p=0.868) and preoperative mam-mography (3.460±0.282, p=0.814), and on applying Lin's concordance correlation coefficient, both modalities showed strong correlation with the final pathology. On correlating between the Tumor-to-Breast Volume (TTBV) ratio and the type of surgery, it was found that breast-conserving surgery can safely be done up to a ratio of about 10%. Conclusion: Sonomammography has shown strong relia-bility in the pre-operative estimation of breast cancer size when compared to the final pathological size. The Tumor-to-Breast Volume Ratio is a very useful tool in surgical planning for treatment of breast cancer.