Determining Much Space a Table Uses

sp_spaceused computes and displays the number of rows and data pages used by a table or a clustered or nonclustered index.

To find out how much space a table uses, enter:
sp_spaceused [objname] 

To display a report on the space used by the titles table:

sp_spaceused titles
name    rows   reserved  data  index_size  unused      
------- -----  --------- ----- ---------   ------
titles  18     48 KB     6 KB  4 KB        38 KB
(0 rows affected)

If you do not include an object name, sp_spaceused displays a summary of space used by all database objects.