As of August 2022, Sigma Alpha Iota included 134,390 initiated members worldwide. A number of different memberships are possible.

Collegiate Membership is available to women in organized chapters at one of over 210 music schools throughout the United States and is by invitation only. Non-students who are trained, active musicians, may also be asked by the college chapter to join this Greek music organization.

Alumnae Membership is available in local area alumnae chapters and through the SAI Alumnae Association.

Patroness Membership is for women who support the arts in the community, and have been invited by a college or alumnae chapter to join SAI.

Distinguished Membership of four types are offered by the National Executive Board:

Member Laureate - an initiated member of the Fraternity who has achieved international distinction in the music profession.

Honorary Member - a woman who has achieved international distinction in the music profession who is not an initiated member of Sigma Alpha Iota.

National Arts Associate - a man or woman who is nationally recognized for distinguished contribution to the arts.

Friend of the Arts - a man or woman who is supportive of and actively involved in the arts at a local or regional level.