sp_spaceused returns number of rows, disk space reserved, and disk space used by a table. However when you have to return the space used by all the tables in a database, you have two options: One is to loop through all the tables and then pass the table name to the sp_spaceused procedure. The second is to use the undocumented sp_MSforeachtable procedure. We will explore both of these over here:
The Lengthy Way


















Note: The advantage in taking the lengthy approach is that you can create another temporary table and sort the tables based on the space used.
The Short Way


Note: sp_MSforeachtable is an undocumented stored procedure
References :
http://msdn2.microsoft.com/en-us/library/ms188776.aspx
http://www.msnewsgroups.net/group/microsoft.public.dotnet.languages.csharp/topic37975.aspx
http://www.mssqlcity.com/Articles/Undoc/SQL2000UndocSP.htm