User blog comment:B214/Volume 23 discussion blog/@comment-1359322-20170220174230/@comment-2208155-20170223152524

Ultimate Pawn.. Very entertaining this answer.

Issei confirmed that Grayfia Bust is bigger than Rias in the Let´s Go Onsen:

A body in the same league as Rias…..no, the reality where a body which surpasses her is right next to me!

https://www.baka-tsuki.org/project/index.php?title=High_School_DxD:Dragon_Magazine_2013-02#Part_3

In another anime One Piece.. The Biggest Human bust is 111.. With the measures of Rias and Akeno I would not be surprised that Grayfia is between 105-108 ..