Pyrodiversity likely begets biodiversity in many ecosystems, yet no consensus surrounds how best to quantify the phenomenon and its drivers remain largely untested. We present a generalizable functional diversity approach for measuring pyrodiversity, which incorporates multiple fire regime traits and can be applied across scales. Further, we tested the socioecological drivers of pyrodiversity among forests of the western United States. Largely mediated by burn activity, pyrodiversity was positively associated with actual evapotranspiration, climate water deficit, wilderness designation, elevation, and topographic roughness but negatively with human population density. These results indicate pyrodiversity is maintained in productive areas with strong annual dry periods and minimal fire suppression. This novel approach along with an improved understanding of pyrodiversity's drivers can facilitate future studies investigating how the pyrodiversity-biodiversity relationship varies among taxa, regions, and fire regimes.