Background: Right-sizing instrument trays reduce processing and replacement costs, physical strain, and turnover times. Historically, a 98-instrument head and neck tray has been used for breast lumpectomy cases at our institution. Observations revealed that many instruments on the tray were not used during the breast cases. With the significant number of surgical breast lumpectomies performed annually, tray downsizing could significantly reduce costs and physical strain. Methods: Surgical technicians identified instruments needed for a standard breast lumpectomy. Breast surgeons reviewed the list and made final recommendations. Three of 13 existing head and neck trays were converted to breast lumpectomy trays. The number of breast lumpectomies in 2017 was pulled from the institution's health information system. Instrument quantities were verified using instrument management software. Weights were taken on a digital scale, and processing cost was estimated by a consultant. Results: The new breast trays included 51 instruments rather than the standard 98-instrument trays. Reprocessing cost decreased from $49.98 to $26.01. With 449 breast lumpectomies performed at the institution in 2017, the annual reprocessing savings totaled $10,763. The tray weight was reduced from 27 to 16 pounds. Setup time decreased from 7 to 4 min per use (22.5 h saved annually). Conclusions: Downsizing from a head and neck tray to a specific breast lumpectomy tray demonstrated a reduction in reprocessing cost, tray weight, and setup time. Lighter trays allow for safer handling and transport by surgical personnel. In the current health-care environment, it is important to maximize operating room efficiency and minimize cost.