The mean specimen density was 0.942 ± 0.022 g/ml for breast tissue and 0.935 ± 0.021 g/ml for abdominal tissue, showing no significant difference (p = 0.230). Breast tissue density significantly (p= 0.04) decreased with age, while abdominal tissue did not. A regression equation to calculate the density of breast tissue corrected for age [breast density (g/ml) = 0.975 - 0.0007 * age] is provided. Breast tissue density was not related to BMI, past pregnancy or a history of breastfeeding. The breast implants had a density ranging from 0.755 g/ml to 1.031 g/m which differed significantly from breast tissue density (-0.186 g/ml (-19.8%) to +0.090 g/ml (+9.58%); p= <0.001) Conclusion: Our results support the suitability of abdominal based perforator flaps in achieving both volume and weight symmetry in unilateral autologous breast reconstruction. Abdominal flap volume can be derived one-to-one from mastectomy weight. Further, given significant brand-dependent density differences, the potential to impose weight disbalances when performing unilateral implant-based reconstructions of large breasts should be considered.