Oracle : How to Check free memory in your SGA

rem -----------------------------------------------------------------------
rem Filename: sga_free.sql
rem Purpose: Reports free memory available in the SGA
rem Date: 09-Jun-1998
rem Author: Frank Naude, Oracle FAQ
rem -----------------------------------------------------------------------

select f.inst_id,pool,name,
sgasize/1024/1024 "Allocated (M)",
bytes/1024 "Free (K)",
round(bytes/sgasize*100, 2) "% Free"
from (select sum(bytes) sgasize from sys.gv_$sgastat) s, sys.gv_$sgastat f
where f.name = 'free memory'
/