calculating tables size in Oracle

calculate_more_power.sql

COLUMN TABLE_NAME FORMAT A32
COLUMN OBJECT_NAME FORMAT A32
COLUMN OWNER FORMAT A10

SELECT
   owner, table_name, TRUNC(sum(bytes)/1024/1024) Meg
FROM
(SELECT segment_name table_name, owner, bytes
 FROM dba_segments
 WHERE segment_type = 'TABLE'
 UNION ALL
 SELECT i.table_name, i.owner, s.bytes
 FROM dba_indexes i, dba_segments s
 WHERE s.segment_name = i.index_name
 AND   s.owner = i.owner
 AND   s.segment_type = 'INDEX'
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.segment_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBSEGMENT'
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.index_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBINDEX')
WHERE owner in UPPER('&owner')
GROUP BY table_name, owner
HAVING SUM(bytes)/1024/1024 > 10  /* Ignore really small tables */
ORDER BY SUM(bytes) desc
;

calculate_table_size_oracle.sql

select owner ||'.' || table_name as table_name,
round((num_rows * avg_row_len)/1024/1024,2) as MB,
initial_Extent
from all_tables
where blocks is not null and not owner in ('SYS', 'SYSTEM') 
order by MB desc

calculate_with_shrink_command.sql

select  
round((t.num_rows * t.avg_row_len)/1024/1024,2) as MB,
round(((t.blocks - t.empty_blocks) * 8192)/1024/1024,2) as MB_BLOCKS,
t.num_rows as linhas, 
'alter table ' ||t.owner || '.' || t.table_name || ' move storage(initial 64k next 64k pctincrease 0);'
from all_tables t
where t.blocks is not null and not owner in ('SYS', 'SYSTEM') 
order by MB desc

When I say count(*) it displays "204457898" records as count .... but when calculate_table_size_oracle.sql ... it gives number of rows as "185527835"... so your how to deciper this?

num_rows and avg_row_len - not real current values, but only stats that updated by 'ANALYZE TABLE your_table COMPUTE STATISTICS'.