MPGs by Career Order of their Bestselling Album.

[slw84]

Took me a second to understand this metric.

[Soda Pop Queen]

Madonna's best-selling main studio album is True Blue with ~25 million and Beyoncé's best-selling main studio album (solo) is Dangrously in Love with ~11 million. 

[Kool_Aid_King]

You forgot Destiny's Child and Lorde, but this is interesting.