Got a q on the size of a schema

I just ran dbms_stats on a schema.
The db block size is 4096
a query on the dba_tables tells me there are no empty blocks on any table int the schema

I do the following sum select sum(blocks)*1024 from dba_tables where owner = 'SCHEMA_NAME'

It comes back with 531415040

I then do the following query

select count(bytes) from dba_extents where owner = 'SCHEMA_NAME'

this comes back with 958201856


I would expect these two to bring back the same value for the schema size.

Does the second query take statistics and indexes in acount where the first one does not?

What am I missing and which one of the above would be a more accurate way of working out the size of a schema.