Recent studies implicating periodontitis as a cause of systemic diseases have reported that the surface area of periodontal pockets exposed to bacterial biofilm ranges from 50 cm2 to 200 cm2. Since the root surface area of the typical human dentition (excluding 3rd molars) is 75 cm2, these estimates appear too large. The goal of this study was to relate linear periodontal probing measurements to the dentogingival surface area (DGES). The DGES comprises both the sulcular and junctional epithelium, present in health, as well as any intervening pocket epithelium present in periodontitis. Formulas to estimate the DGES from clinical measures were derived from a meta-analysis of root surface areas, published values of root length, and a study that related the percent remaining root surface area to the percent remaining root length. These formulas were applied to a survey of the adult US population, the Veterans Affairs (VA) Dental Longitudinal Study, and a population of individuals visiting a periodontist. Individuals without periodontitis had a typical DGES of 5 cm2. Among individuals with periodontitis, the mean DGES in the three samples ranged from 8 cm2 (ranging from 1 cm2 to 29 cm2) to 20 cm2 (ranging from 2 cm2 to 44 cm2). It was concluded that the mean DGES among individuals with periodontitis ranges from 8 cm2 to 20 cm2, considerably smaller than the range of 50 cm2 to 200 cm2 currently assumed.