It really depends on how you define aphantasia. Often the VVIQ score is used, a vividness score ranging from 16 to 80.

About 0,8 % of people have a score of 16, and 3,9 % have a score <= 32. The figures are from one of the more recent studies. Other studies report similar figures, for example one study by Zeman found 0,7 % with a score of 16.

About ¼ of all people with visual aphantasia also have multisensory aphantasia (all classical senses and emotions).