Abstract: AlloDerm has been used as a tissue supplement in conjunction with the pectoralis major muscle to provide full coverage over an implant in breast reconstruction. While this method of reconstruction has shown promising results there is little known on the relationship of AlloDerm size and potential immediate expansion volume. A retrospective chart review was completed evaluating all tissue expander or primary implant reconstructions using AlloDerm. Data recorded included: The type/size of implant/expander, dimensions of the AlloDerm used, initial fill volume, number of expansions and time period of expansion. Statistical analysis was completed with a linear regression model. AlloDerm was used on 49 patients (72 reconstructions). Thirty-four patients (50 reconstructions) underwent reconstruction with a tissue expander and 15 patients (22 reconstructions) underwent a single stage reconstruction with a permanent implant. The tissue expander volume filled (cc) could be predicted by 5 × surface area of AlloDerm (cm2) − 12 (R2 = 0.62) and 80 × height of AlloDerm (cm) − 15 (R2 = 0.59). The tissue expanders could be filled to an average of 75% of total size and required three to four injections in the postoperative period to reach full expansion. Obviously, a requirement for maximal implant expansion is an appropriate skin sparing mastectomy. There is a mathematical relationship between fill volume and surface area as well as height of AlloDerm used in breast reconstruction. This analysis provides a guideline for immediate implant expansion to surgeons using AlloDerm in reconstructive breast surgery.