Gynaecomastia is a common condition with prevalence in young adults as high as 38%. Enlarged breasts can cause anxiety, self-consciousness and embarrassment, functional problems and psychosocial discomfort and fear of malignancy. There are many surgical techniques for treating Gynaecomastia according to its grade. The aim of this study was to assess our novel calculation to adjust round block excision to minimize complication and difficulties of this procedure.   Patients and methods: This was a prospective study conducted on thirty-three patients (forty-two breasts) with grade IIB and III gynaecomastia “Simon grading" undergoing mastectomy via calculated round block excision.   Conclusion: Our novel calculated round block excision provides a safe and feasible technique for mastectomy in large gynaecomastia grades IIB and III.