Introduction: Two-stage implant based breast reconstruction remains the most commonly performed post-mastectomy reconstruction. While prior studies have explored the relationship between tissue expander (TE) features and permanent implant (PI) size in subpectoral reconstruction, recent trends have demonstrated a shift towards prepectoral implant placement with acellular dermal matrix (ADM). This study aims to identify pertinent TE characteristics and evaluate their correlations with PI size for prepectoral implant-based reconstructions. Materials and Methods: This study analyzed patients who underwent two-stage prepectoral tissue expansion for breast reconstruction followed by implant placement at single institution. Exclusion criteria were delayed, autologous, and direct-to-implant breast reconstruction patients. Clinical and demographic patient data were collected for the cohort. TE and PI features were recorded, along with mean TE size, PI size, and mean mastectomy weights. Significant predictors for PI volume were identified with regression analysis. Results: We identified 177 patients and 296 breast reconstructions that met the inclusion criteria. Multivariate analysis identified significant variables for PI size prediction, including mastectomy weight (R2=0.42; p<0.0001), TE size (R2=0.60; p<0.0001), and TE final fill (R2=0.57; p<0.0001). The prediction expression was calculated to model the correlation: PI size = 26.6 + 0.38*(TE final fill) + 0.61*(TE size). Conclusion: Tissue expander size, final expansion volume, and mastectomy weight were significant variables for implant size prediction. The formula yielded significant regression coefficient values for TE size and final fill. With prepectoral implant placement gaining popularity, this algorithm may help optimize preoperative planning for prepectoral reconstructions.