Find size of tables in Oracle DB

For some tables in GB:-
select SUM(BYTES/1024/1024/1027) GB from  user_segments where SEGMENT_NAME in ('ALC_AVAILABILITY_MATRIX_28MAY','ALC_AVAILABILITY_MATRIX_11JUN','ALC_AVAILABILITY_MATRIX_M28','ALC_AVAILABILITY_MATRIX_J11','ALC_POP_A02','ALC_POP_D11','ALC_POP_F05','ALC_POP_J22','ALC_POP_M05','ALC_POP_M19','DH_VAB_ADDRESS_DETAIL_A30','DH_VAB_ADDRESS_DETAIL_J09','DH_VAB_ADDRESS_MASTER_09J','DH_VAB_ADDRESS_MASTER_J09','DH_VAB_CITY_DETAIL_05M','DH_VAB_CITY_DETAIL_28M','DH_VAB_CITY_DETAIL_A30','DH_VAB_CITY_DETAIL_M05','DH_VAB_CITY_DETAIL_M28','DH_VAB_CITY_MASTER_28M','DH_VAB_CITY_MASTER_M28','DH_VAB_PHONE_DETAIL_19F','DH_VAB_PHONE_DETAIL_M28','DH_VAB_PHONE_MASTER_19F','DH_VAB_POSTAL_DETAIL_05M','DH_VAB_POSTAL_DETAIL_19M','DH_VAB_POSTAL_DETAIL_M05','DH_VAB_POSTAL_DETAIL_19M','DH_VAB_POSTAL_MASTER_05M','DH_VAB_POSTAL_MASTER_19M','DH_VAB_POSTAL_MASTER_M05','DH_VAB_POSTAL_MASTER_M19');

Finding total tables:-
select table_name from user_tables;






Finding size of All tables in GB:-
select SUM(BYTES/1024/1024/1024) GB from  user_segments where SEGMENT_NAME in (select table_name from user_tables);