Prachuap Khiri Khan covers an area totaling . The province is on the Kra Isthmus, the narrow land bridge connecting the Malay Peninsula with mainland Asia. The province has the narrowest part of Thailand, just from the Gulf of Thailand to the border with Myanmar in the Tenasserim Hills. Geographically, Prachuap Khiri Khan is a moderate plain with elevations varying from sea level to . The maximum elevations are found in the northeastern and central west regions, which make up approximately 30 percent of the province.