Block count usage by a table

I see the following query mentioned to find out how many blocks a table is using up:

select COUNT(DISTINCT(SUBSTR(ROWID,1,8)||SUBSTR(ROWID,15,4)))

      Blocks_Used
 from sometable;

If most/all of the rows are chained/migrated, won't this query be inaccurate? Received on Sun Jul 05 1998 - 22:08:02 CDT