This subject covers attempts to rank Christian denominations and communions by size. Such lists are used by scholars, journalists and religious organizations to convey relative influence, but they rest on differing definitions of "membership" and a mix of self-reported and independent data. Readers should treat any single ranked table as an approximation rather than a definitive census.

Methodology and definitions

Different sources count members in different ways: baptized or registered members, adults who self-identify with a denomination, regular worshippers, or all people on a denomination's rolls (which can include children and non-practicing affiliates). Data may come from church authorities, national censuses, surveys, or academic estimates. Because of these variations, a denomination that records everyone ever baptized may appear larger than one that reports only active participants.

Major groupings and typical rankings

  • Roman Catholic Church — universally recognized as the largest single Christian body, organized as a global communion under the Pope.
  • Eastern Orthodox — a family of autocephalous (self-governing) churches that together constitute one of the largest Christian traditions.
  • Anglican Communion — a worldwide communion of churches historically linked to the Church of England; frequently appears high on lists when aggregated.
  • Protestant traditions — include many denominations (Lutheran, Methodist, Baptist, Presbyterian, Pentecostal and others); if counted collectively they form a very large segment, but individual denominations vary widely in size.
  • Oriental Orthodox and other Eastern bodies — distinct ancient churches with sizable national followings in parts of Africa and Asia.
  • Restorationist and newer movements — groups such as Latter-day Saints and Jehovah's Witnesses report membership figures and are frequently listed among sizeable denominations.

Because denominational boundaries can be fluid (schisms, mergers, national churches, and independent congregations), lists must decide whether to aggregate by communion, tradition, or organizational membership. For example, "Pentecostalism" may be treated as a movement spanning many denominations rather than a single body.

Uses, limitations and notable issues

These rankings are useful for demographic studies, ecumenical planning, and historical comparison. However, analysts warn about double-counting (when people belong to more than one group), inconsistent reporting periods, and political or institutional incentives that encourage inflation or conservative reporting. The most reliable approach is to compare multiple sources—denominational reports, national censuses and independent research—and to note the counting method used.