 A Bahá 'í published document reported 4 @.@ 74 million Bahá 'ís in 1986 growing at a rate of 4 @.@ 4 % . Bahá 'í sources since 1991 usually estimate the worldwide Bahá 'í population to be above 5 million . The World Christian Encyclopedia estimated 7 @.@ 1 million Bahá 'ís in the world in 2000 , representing 218 countries , and 7 @.@ 3 million in 2010 with the same source . They further state : " The Baha 'i Faith is the only religion to have grown faster in every United Nations region over the past 100 years than the general population ; Baha ’ i was thus the fastest @-@ growing religion between 1910 and 2010 , growing at least twice as fast as the population of almost every UN region . " This source 's only systematic flaw was to consistently have a higher estimate of Christians than other cross @-@ national data sets . 
