The U.S. government estimates the country’s total population at 33.6 million (midyear 2019 estimate), including more than 12 million foreign residents. Between 85 and 90 percent of the approximately 20 million citizens are Sunni Muslims.

Shia Muslims constitute 10 to 12 percent of the citizen population and at least one-quarter of the Eastern Province’s population. Approximately 80 percent of Shia are “Twelvers” (Shia who recognize 12 imams) and are primarily located in the Eastern Province. The Nakhawala, or “Medina Shia,” are also Twelvers and reside in small numbers in the western Hejaz region. Estimates place their numbers at approximately 1,000. Twelver Shia adhere to the Ja’afari school of jurisprudence. Most of the remaining Shia are Sulaimani Ismailis, also known as “Seveners” (those who branched off from the Twelvers to follow Isma’il ibn Ja’afar as the Seventh Imam). Seveners number approximately 500,000 and reside primarily in Najran Province, where they probably constitute a majority of the province’s inhabitants. Another branch of Sevener Shia, the Bohra Ismailis, probably number at least a few hundred, most of whom are of South Asian origin. Pockets of Zaydis, members of another branch of Shia Islam, numbering a total of approximately 20,000, reside primarily in the provinces of Jizan and Najran along the border with Yemen.

Foreign embassies indicate the noncitizen population, including many undocumented migrants, is mostly Muslim. According to a 2010 survey by the Pew Research Center, of the country’s total population (including foreigners), there were approximately 25.5 million Muslims, 1.2 million Christians (including Eastern Orthodox, Protestants, and Roman Catholics); 310,000 Hindus; 180,000 religiously unaffiliated (including atheists, agnostics, and individuals who did not identify with any particular religion); 90,000 Buddhists; 70,000 followers of folk religions; and 70,000 adherents of other religions.