User blog comment:B214/Volume 23 discussion blog/@comment-1359322-20170220174230/@comment-9595671-20170223175923

If Grayfia's bigger than Rias atleast, then she's atleast at 100cm at the smallest, if only Issei mentioned they exceeded Akeno's too we'd have a good idea what size she was at. She could be bigger than Akeno, but she might not be either.

Gabriel's gotta be the biggest though considering how much Azazel hyped them, and unless I missed another time he did this, Gabriel's breasts were the only time he's ever mentioned breasts and generalizing them to a specific indivividual instead of as a whole.