This article gives information about the relative size of denominations, based mainly on claims by the churches themselves.
Christian denominational families
Christianity – 2.51 billion
Catholicism – 1.329 billion
Catholicism is the largest branch of Christianity with 1.329 billion and the Catholic Church is the largest among churches. Figures below are in accordance with the Annuario Pontificio, at 2018. The total figure does not include independent Catholic denominations (18 million).
Latin Church – 1.311 billion
Eastern Catholic Churches – 18 million
Byzantine Rite – 8.2 million
Ukrainian Greek Catholic Church – 5.5 million
Melkite Greek Catholic Church – 1.6 million
Romanian Greek Catholic Church – 0.5 million
Ruthenian Greek Catholic Church – 0.4 million
Hungarian Greek Catholic Church – 0.3 million
Slovak Greek Catholic Church – 0.3 million
Belarusian Greek Catholic Church – 0.1 million
Italo-Albanian Catholic Church – 0.01 million
Greek Catholic Church of Croatia and Serbia – 0.01 million
Georgian Byzantine Catholic Church – 0.01 million; Albanian Greek Catholic Church – 0.01 million Russian Greek Catholic Church – 0.01 million Macedonian Greek Catholic Church – 0.001 million Bulgarian Greek Catholic Church – 0.001 million Greek Byzantine Catholic Church – 0.001 million East Syriac Rite – 4.9 million Syro-Malabar Catholic Church – 4.3 million Chaldean Catholic Church – 0.6 million West Syriac Rite – 4.2 million Maronite Church – 3.5 million Syro-Malankara Catholic Church – 0.5 million Syriac Catholic Church – 0.2 million Armenian Rite – 0.8 million Armenian Catholic Church – 0.8 million Alexandrian Rite – 0.5 million Coptic Catholic Church – 0.2 million Eritrean Catholic Church – 0.2 million Ethiopian Catholic Church – 0.1 million
Canonically irregular groups
Society of Saint Pius X – 1 million (claimed)
Independent Catholicism – 18 million
Various denominations self-identifying as Catholic, despite not being affiliated with the Catholic Church.
Philippine Independent Church – 6 million (Part of the Anglican Communion) Chinese Patriotic Catholic Association – 6 million Brazilian Catholic Apostolic Church – 5 million Traditionalist Mexican-American Catholic Church – 2 million Old Catholic Church – 0.1 million (Part of the Anglican Communion) Polish National Catholic Church – 0.03 million Apostolic Catholic Church – 0.005 million Palmarian Catholic Church – 0.002 million
Protestantism – 900 million
Protestantism is the second largest major group of Christians by number of followers. Estimates vary from 800 million to a billion, or nearly 40% of all Christians. The main reason for this wide range is the lack of a common agreement among scholars as to which denominations constitute Protestantism. For instance, most sources but not all include Anabaptism, Anglicanism, Baptists and Independent Nondenominational Christianity as part of Protestantism. Moreover, Protestant denominations altogether do not form a single structure comparable to the Catholic Church, or to a lesser extent the Eastern Orthodox Communion. However, several different comparable communions exist within Protestantism, such as the Anglican Communion, World Communion of Reformed Churches, World Baptist Alliance, World Methodist Council and the World Lutheran Federation. Regardless, 900 million is the most accepted figure among various authors and scholars, and thus is used in this article. Note that this 900 million figure also includes Anglicanism, as well as Anabaptists, Baptists and multiple other groups that might sometimes disavow a common "Protestant" designation, and would rather prefer to be called, simply, "Christian".
Historical Protestantism – 300–400 million
The number of individuals who are members of historical Protestant Churches totals to 300-400 million.