SQL> select tablespace_name, sum(bytes) / 1024 / 1024 from dba_data_files group by tablespace_name;
TABLESPACE_NAME        SUM(BYTES)/1024/1024
------------------------------ --------------------
UNDOTBS1                    100
SYSAUX                     530
USERS                       5
SYSTEM                     700
EXAMPLE                     100
5 rows selected

SQL> select tablespace_name, sum(bytes) / 1024 / 1024 from dba_free_space group by tablespace_name; 
TABLESPACE_NAME        SUM(BYTES)/1024/1024
------------------------------ --------------------
SYSAUX                    26.125
UNDOTBS1                  69.6875
USERS                    0.9375
SYSTEM                    1.1875
EXAMPLE                    21.25
5 rows selected