the following code will help to u to know the exact values i.e. used unused Actually used etc.

set linesize 121
---------------------------------------------------------------------------------------
-- free.sql
--
-- This SQL Plus script lists freespace by tablespace
----------------------------------------------------------------------------------------

column dummy noprint
column pct_used format 999.9 heading |Used
column name format a19 heading Tablespace Name
column Kbytes format 999 999 999 heading Kbytes
column used format 999 999 999 heading Used
column free format 999 999 999 heading Free
column largest format 999 999 999 heading Largest
column max_size format 999 999 999 heading MaxPoss|Kbytes
column pct_max_used format 999. heading |Max|Used
break on report
compute sum of kbytes on report
compute sum of free on report
compute sum of used on report

select (select decode(extent_management 'LOCAL' '*' ' ') ||
decode(segment_space_management 'AUTO' 'a ' 'm ')
from dba_tablespaces where tablespace_name b.tablespace_name) ||
nvl(b.tablespace_name
nvl(a.tablespace_name 'UNKOWN')) name
kbytes_alloc kbytes
kbytes_alloc-nvl(kbytes_free 0) used
nvl(kbytes_free 0) free
((kbytes_alloc-nvl(kbytes_free 0))/
kbytes_alloc)*100 pct_used
nvl(largest 0) largest
nvl(kbytes_max kbytes_alloc) Max_Size
decode( kbytes_max 0 0 (kbytes_alloc/kbytes_max)*100) pct_max_used
from ( select sum(bytes)/1024 Kbytes_free
max(bytes)/1024 largest
tablespace_name
from sys.dba_free_space
group by tablespace_name ) a
( select sum(bytes)/1024 Kbytes_alloc
sum(maxbytes)/1024 Kbytes_max
tablespace_name
from sys.dba_data_files
group by tablespace_name
union all
select sum(bytes)/1024 Kbytes_alloc
sum(maxbytes)/1024 Kbytes_max
tablespace_name
from sys.dba_temp_files
group by tablespace_name )b
where a.tablespace_name (+) b.tablespace_name
order by 1
/

Hi

can u plz explain me in detail abt the size of tablespace not the code

but i need a theoritical explanation

im waiting for ur reply

according to my knowledge concern that is depend on Organization data size ( by estimating the no of tables and No. of rows in one Year two year Three year i.e.

Step 1 : categorize total Data table you want to create ie. Dynamic Semi-dynamic Static. Etc . -This is you can by observing Data Table behavior in different time spans with in a year.

Step: 2: Estimate the tables an find the Average Row Length (ARL). Using pl/sql library.

Step 3: No of rows estimate with in the 1 2 and 3 years.

Step 4: Calclulate the Total Size (tables x Row Length x No of rows require in 3 years)

Step 5: Depending on that we can come to the point to estimate the size of tablespace require.

we can estimate the size of the tablespace from the number of datafiles going to attach with it or you can use dba_data_files view to find the size for the particular tablespace....

it depends on how many .dbf files u r going to store it will be ur size of data
oracle recommends if one .dbf file size exceeds size of 2gb then we have to create a new .dbf etension file . it is the physical file while tablespace is logical storage area containing segments