How do I indicate that I am citing an album in 33 rpm format?

Note: This post relates to content in the eighth edition of the MLA Handbook. For up-to-date guidance, see the ninth edition of the MLA Handbook.

List album formats, if needed, in the optional-element slot at the end of your works-cited-list entry:

Sinatra, Frank. The Voice: Columbia Years, 1943-1952. Columbia Records, 1986. 6 LP, 33 rpm box set.

Snail Mail. “Thinning.” Habit, Sister Polygon Records, 2016. Vinyl EP.