Oracle queries to get size info

Query To get size of all the tables/indexes that are present in specific user

SELECT
  segment_name,
  segment_type,
  SUM (BYTES)/ (1024 * 1024 * 1024) sizegb
    FROM user_segments
GROUP BY segment_name, segment_type
ORDER BY sizegb DESC, segment_type, segment_name;

scriptoutput

SEGMENT_NAME          SEGMENT_TYPE        SIZEGB
--------------------------------------------------------------------------------------------------------
BL1_CHARGE_CYCLE      TABLE                        0.360015869140625
BL1_CHARGE                   TABLE PARTITION     0.34429931640625
BL1_TAX_ITEM                TABLE PARTITION     0.150054931640625

Query To get available Tablespace sizes

SELECT b.tablespace_name, ROUND (tbs_size, 2) size_gb, a.free_space free_gb
  FROM (SELECT   tablespace_name,
                 ROUND (SUM (BYTES) / 1024 / 1024 / 1024, 2) AS free_space
            FROM dba_free_space
        GROUP BY tablespace_name) a,
       (SELECT   tablespace_name, SUM (BYTES) / 1024 / 1024
                                  / 1024 AS tbs_size
            FROM dba_data_files
        GROUP BY tablespace_name
        UNION
        SELECT   tablespace_name, SUM (BYTES) / 1024 / 1024 / 1024 tbs_size
            FROM dba_temp_files
        GROUP BY tablespace_name) b
 WHERE a.tablespace_name(+) = b.tablespace_name;

scriptoutput

TABLESPACE_NAME          SIZE_GB         FREE_GB
----------------------------------------------------------------------------
POOL_DATA                108.89              30.04
POOL_IX                      29.3                 16.19
SYSTEM                      1.46                 0.9
UNDOTBS                   17.58                17.54
TEMP                          14.65