Health care facility surge capacity has received significant planning attention recently, but there is no commonly accepted framework for detailed, phased surge capacity categorization and implementation. This article proposes a taxonomy within surge capacity of conventional capacity (implemented in major mass casualty incidents and representing care as usually provided at the institution), contingency capacity (using adaptations to medical care spaces, staffing constraints, and supply shortages without significant impact on delivered medical care), and crisis capacity (implemented in catastrophic situations with a significant impact on standard of care). Suggested measurements used to gauge a quantifiable component of surge capacity and adaptive strategies for staff and supply challenges are proposed. The use of refined definitions of surge capacity as it relates to space, staffing, and supply concerns during a mass casualty incident may aid phased implementation of surge capacity plans at health care facilities and enhance the consistency of terminology and data collection between facilities and regions.