size /1024 / 1024 AS gbsize
That is not the right computation to get gb. "size" is the number/count of 8K pages. So, to get gb from size, you need to do this calc:
CAST(size / 128.0 / 1024 AS int) AS gbsize
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.