PURPOSE: Predicting the change in breast size for a specific patient's need is a challenging problem in breast augmentation. We intended to investigate the post-augmentation degree of breast size according to the size of cohesive silicone gel implant. METHODS: To predict post-augmentation breast size, we measured 100 patients' pre-and postoperative 3 month's bust circumference. All patients were performed by total subfascial breast augmentation with moderate profile cohesive silicone gel implant through areolar omega (transareolar-perinipple) incision. RESULTS: According to this study, each additional one pair of 100mL in implant size yielded an approximate 1.5cm increase in bust circumference(p=0.006). CONCLUSION: From this result, we conclude that each additional one pair of 100mL in implant volume yielded about 1.5cm increase in bust circumference. Although this result may not be applied to every patient, we believe that it yields a practical chart that can help to predict the amount of increase in breast size with the use of cohesive silicone gel implant of a specific size preoperatively.