This documentation details the U.S. Fire Administration’s (USFA’s) current fire data estimation methodology for all building (i.e., residential and nonresidential) fires and associated losses. The documentation consists of three sections: (1) An overview of national estimates that defines what national estimates are; describes the overall approach and methodology used to derive them; and summarizes the basic issues with this current, accepted approach. This national estimates methodology serves as the basis for the computation of USFA’s building fire estimates; (2) A discussion of what is meant by "buildings" versus "structures" and the implications these classifications have on deriving estimates of the fire problem that are meaningful to the public and prevention efforts, and (3) A step-by-step methodology which describes how USFA computes national estimates of building fires and associated losses using data from USFA’s National Fire Incident Reporting System (NFIRS) and estimates from the National Fire Protection Association’s (NFPA’s) annual Survey of Fire Departments for U.S. Fire Experience. Formulas for each type of estimate, 32 in all, are given.