How much space is needed for Oracle sorting?

We are experiencing running out of tablespace when we are performing
'order by's' in select's.

In my testing, I found that I need anywhere from 3-4 times the table size in my sort tablespace to perform the select(and inherant sort).

I calculated my tablesize by multiplying average_rowlenth * number_of_rows
gathered from an analyze table. I deduced the sort size by running the
'order by' query and monitoring the sys.dba_free_space view.

Any 'real life' experiences with tablespace needed for sorts?

Scott Overby                                         scoverby_at_delphi.com