Query tablespace size and usage

select fs.tablespace_name                      "Tablespace",
   (df.totalspace - fs.freespace)              "Used MB",
   fs.freespace                                "Free MB",
   df.totalspace                               "Total MB",
   round(100 * (fs.freespace / df.totalspace)) "Pct. Free"
from (select
      tablespace_name,
      round(sum(bytes) / 1048576) TotalSpace
   from dba_data_files
   group by tablespace_name) df,
   (select tablespace_name, round(sum(bytes) / 1048576) FreeSpace
   from dba_free_space
   group by tablespace_name) fs
where df.tablespace_name = fs.tablespace_name;