Size of a table containing Blob column

Hi ,
I need to find out the Size of a table containing Blob column along with other columns. I am new to Blobs so Im not able to understand the concept of using dbms_lob.getlength to find this out.
My table Customers is as follows:

( Name varchar2(120),
Ord_dt Date,
Ord_summary Blob)

It contains 1000 records. Now how do I find out the size of this table ? Do I have to calculate the varchar and date column separate from the BLOB column ? Any help is appreciated.

Thanks

query dba_segments

select sum(bytes) from dba_segmets where table_name = 'CUSTOMERS'

This is not the recommended way to calculate the size of the tables containing BLOB.
Thats what Im trying to find out.

If size of blob column cross 4k, then oracle store blob column separate from the parent table.

Hope this gives some idea

NO this doesnt give any ideas. It doesnt answer the question.