Tablespaces that are >=80% full, and how much to add to make them 80% again

set pages 999 lines 100
col "Tablespace" for a50
col "Size MB"  for 999999999
col "%Used"  for 999
col "Add (80%)"  for 999999
select tsu.tablespace_name "Tablespace"
, ceil(tsu.used_mb) "Size MB"
, 100 - floor(tsf.free_mb/tsu.used_mb*100) "%Used"
, ceil((tsu.used_mb - tsf.free_mb) / .8) - tsu.used_mb "Add (80%)"
from (select tablespace_name, sum(bytes)/1024/1024 used_mb
 from    dba_data_files group by tablespace_name) tsu
,  (select ts.tablespace_name
 ,       nvl(sum(bytes)/1024/1024, 0) free_mb
 from    dba_tablespaces ts, dba_free_space fs
 where   ts.tablespace_name = fs.tablespace_name (+)
 group by ts.tablespace_name) tsf
where tsu.tablespace_name = tsf.tablespace_name (+)
and 100 - floor(tsf.free_mb/tsu.used_mb*100) >= 80
order by 3,4
/