Oracle tablespace size

gistfile1.sql

select	a.TABLESPACE_NAME,
	a.BYTES bytes_used,
	b.BYTES bytes_free,
	b.largest,
	round(((a.BYTES-b.BYTES)/a.BYTES)*100,2) percent_used
from 	
	(
		select 	TABLESPACE_NAME,
			sum(BYTES) BYTES 
		from 	dba_data_files 
		group 	by TABLESPACE_NAME
	)
	a,
	(
		select 	TABLESPACE_NAME,
			sum(BYTES) BYTES ,
			max(BYTES) largest 
		from 	dba_free_space 
		group 	by TABLESPACE_NAME
	)
	b
where 	a.TABLESPACE_NAME=b.TABLESPACE_NAME
order 	by ((a.BYTES-b.BYTES)/a.BYTES) desc;