User blog comment:B214/Question and Answers 6/@comment-71.15.104.27-20180422153017/@comment-28884330-20180430223803

Judging by his height difference with Rias in the Volume 10 illustration, considering that Rias is 172 cm tall, I'd say Sairaorg probably reaches to around 2 meters, with a minimum of 190 cm, which is REALLY tall.