This script calculates the average row size for all tables in a schema.
It generates a script (getAvgCol.sql) from USER_TABLES and then runs it.
The following type of SELECT is generated for each table in USER_TABLES:

SELECT round(avg(nvl(vsize(COL1),0)) +
round(avg(nvl(vsize(COL2),0)) + … +
round(avg(nvl(vsize(COLn),0))

Where n=# of cols. on the table

Tables with LONG and LOB columns will not report row size properly. Also
tables with object types will throw the following error and will also not
report row size properly:

ORA-00932: inconsistent datatypes

=============
Sample Output
=============
ACCOUNTS 6
ACCTS 39
ACCT_ADDRS 38
BAD_DATA 116
BASE1 6
BONUS
CEG1 11
CHESS_SAVE
CHESS_SAVE_PLAYER
CITIES 36
COMPANY_SUMMARY 60
CR_FILES 113

Script:

SET ECHO off
REM NAME:   ROWSZ.SQL

drop table column_counts;
create table column_counts
        (
        table_name,
        column_count
        )
        as
        (
        select table_name, max(column_id)
        from user_tab_columns
        where data_type not like 'LONG%' AND table_name in
        (select table_name from user_tables)
        group by table_name
        )
        ;
set pages 0
set tab on
set trim on
set verify off
set feedback off
set termout off
set head off
set lines 100
set recsep off
set embedded on
spool getavgcol.sql
prompt column TB format A30
prompt set head off recsep off
prompt set lines 80 feedback off pages 0
prompt spool getavgcol
REM
column select_line format A8
column end_line format A1
column from_stmt format A34 word_wrap
column col_nm format A100
column col_val format A32
column tnm1 noprint
column tnmprint format A37
column column_id noprint
break on tnm1 skip 2
set null ''
clear breaks
select UTC.table_name tnm1,
        decode(column_id,1,'select ' || chr(39) || UTC.table_name || chr(39) ||
                ' TB, ', '        ') ||
        'round(avg(nvl(vsize('||column_name||'),0)),0)' ||
        decode(column_id,column_count, ' row_size from ' || UTC.table_name
             || ';'|| chr(10)||chr(10),
                ' +') col_nm
from user_tab_columns UTC, column_counts CC
where UTC.data_type not like 'LONG%' AND UTC.table_name = CC.table_name
order by UTC.table_name, UTC.column_id;
prompt spool off
prompt exit
spool off
drop table column_counts;
exit