This articles explains you about estimating the space required for a new table or the space required for an existing table. To estimate the space required by a table , following are necessary:

• The average length of a row
• The expected number of rows in the new table or an existing table.
• The Database Block size.
• The Pctfree value for a table.

Data is stored logically in the form of blocks. A database block is the smallest logical building block of a database. Each block can store some data based on its size specified for the tablespace or database as a whole.

A block header is an area used for overhead within the block. Estimate the block overhead for tables to use 90 bytes.  Based on the block size we can calculate the available space for each database block size as The pctfree setting for the table sets the size of the free space that is unused during inserts. Multiply the available space by  the pctfree value to determine how much space is reserved. Subtract that value from the available space in the block to determine how much space is available to hold newly inserted rows. Continue Reading