How to check the size of the table in oracle?

How to check the size in GB?

select sum(bytes/1024/1024/1024) as GB from dba_segments where segment_name='MESSAGE';

        GB
----------
1381.42932


How to check the size in TB?

select sum(bytes/1024/1024/1024/1024) as TB from dba_segments where segment_name='MESSAGE';

        TB
----------
1.34905207