db2 database total size estimation

Hi All,

Kindly please guide me how i can can estimate of total size needed for an application to perform well.

My Logic:
1) To take all the database object details from test environment.
and
a)calculate there row size
select sum(length) from syscat.columns where tabname=?;

then depending upon the row size estimate the tablespace paze size

b)Next step is to to estimate the amount of rows in one page

<PAGESIZE eq 4055 for 4096 > / row size = no. of rows per page

c) Third step is to estimate the no of rows that will come in future years

eq 200000

200000/ < no. of rows per page> = Total page required

d) adding 10 percent for future estimation for that table

Total page required *1.1=total pages needed

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By repeating this i can estimate space requirements for all tablespaces for tables

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Now how can i estimate the index tablespace sizes for each main tables

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I should also consider the space requirement for use temporary tablespaces, temporary tablespace , and bufferpools for each type of page size.

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Kindly guide me better estimate for designing a database for my application.