To find Top segment sizes where we can reclaim space by reorg tables?

select table_name,owner,PARTITIONED,
round((blocks*8),2) tablesize,
round((num_rows*avg_row_len/1024),0) actual_data_size,
(round((blocks*8),2)-round((num_rows*avg_row_len/1024),0)) Difference
from dba_tables