Understanding `dbcc showcontig` Record Size
When you're storing data that is bigger than what fits into the SQL Server's 8k page, like varbinary(max) or varchar(max), it's stored in an row overflow data structure. It seems showcontig doesn't show this data at all according to books online:


  DBCC SHOWCONTIG does not display row-overflow storage information and
  other new off-row data types, such as nvarchar(max), varchar(max),
  varbinary(max), and xml.


It seems showcontig is deprecated too.  Its replacement sys.dm_db_index_physical_stats can be setup to show storage of "off row" data.  SAMPLE or DETAIL seems to show this data best.