How To Obtain The Size Of All Tables In A SQL Server Database

SET NOCOUNT ON 

DBCC UPDATEUSAGE(0) 

-- DB size.
EXEC sp_spaceused

-- Table row counts and sizes.
CREATE TABLE #t 
( 
    [name] NVARCHAR(128),
    [rows] CHAR(11),
    reserved VARCHAR(18), 
    data VARCHAR(18), 
    index_size VARCHAR(18),
    unused VARCHAR(18)
) 

INSERT #t EXEC sp_msForEachTable 'EXEC sp_spaceused ''?''' 

SELECT *
FROM   #t

-- # of rows.
SELECT SUM(CAST([rows] AS int)) AS [rows]
FROM   #t
 
DROP TABLE #t

Reference : http://therightstuff.de/CommentView,guid,df930155-f60f-4f56-ab33-f1352ff091a1.aspx