SELECT
  name,
  space_limit,
  space_used,
  space_reclaimable 
FROM
  v$recovery_file_dest;
-- ===========================>
SELECT
   name,
   floor(space_limit / 1024 / 1024) "Size MB",
   ceil(space_used / 1024 / 1024)   "Used MB"
FROM
   v$recovery_file_dest
order by
   name asc;
-- ===========================>
SELECT
   name,
   ceil( space_limit / 1024 / 1024) size_mb,
   ceil( space_used / 1024 / 1024) used_mb,
   decode( nvl( space_used, 0),0, 0,   ceil ( ( space_used / space_limit) * 100) ) pct_used
FROM
    v$recovery_file_dest
order by
   name desc;
   
-- =====================================================================================================>
NAME                                                                      SIZE_MB    USED_MB   PCT_USED
--------------------------------------------------------------   ----------  -------------   ------------
/flashback                                                                  2048000      18503          1