The number varies according to which number you think of, it seems. Who qualifies as “a follower” is virtually impossible to decide – many who claim to be so disregard much or most of his advice or requirement. He has said that he cannot find a single (true) devotee among the crowds. Nonetheless, his organization and representatives make the most inflated claims for the number of followers, and they exaggerate the number of Sai Baba cCentres and groups in their efforts to gain privileges and other brownie point at the ashrams, who want all possible propaganda materials to publish and broadcast as widely as possible
See some of the various reports on numbers here:-
Comment: The 4000 village programme never materialized, though it was later trumpeted as a programme to help 6000 villages – see here. This also was a one-day wonder – Many invited members of 6000 villages came to a free junket at Prashanthi Nilayam, but when it was over only a handful remained in contact with the Sathya Sai authorities!