Database size and Storage Metrics are mismatching

Hi,

When I look at the storage metrics for one of our SharePoint Web Application root site collection it shows the top sized site as 28.2% of parent and the size as 21178.5 MB. When we calculate the total size of the site collection from that it should 74994 MB. But when I see the size of the content database ( this is the only site collection in this content database) it shows 185661.5 MB as the size and 26852.5 MB as the space available. When I run the report (Disk Usage By Top Tables) on that database it brings the list with dbo.AllDocStreams table at the top (Data - 80333 MB) followed by dbo.AuditData (Data - 48305 MB) followed by dbo.AllUserData (Data - 8593 MB).

3 years back we migrated this SharePoint Web Application from 2007 to 2010.

I saw that the recycle bin has only 30 day worth data. 

How can we reduce the size of the database according to what it shows in the storage metrics? Appreciate any help.

Thanks.

rani