Estimates of the total number of Protestants are very uncertain, but it seems clear that Protestantism is the second largest major group of Christians after Catholicism in number of followers, although the Eastern Orthodox Church is larger than any single Protestant denomination.
Perkiraan jumlah keseluruhan umat Kristen Protestan sangat tidak pasti, namun mazhab Protestan jelas merupakan kelompok umat Kristen terbesar kedua sesudah Gereja Katolik berdasarkan jumlah pengikut (meskipun Gereja Ortodoks Timur jauh lebih besar dari denominasi Protestan yang mana pun).