The following example demonstrates how to estimate storage requirements. Consider a database with a single customer table with three fields:

  • Cust-num — An integer field that is always three digits
  • Name — A character field containing 12–30 characters, with an average of 21 characters
  • Start-date — A date field

If the table is indexed on just one field (Name) and you expect to have about 500,000 records in the customer table, the following table lists formulas (and examples) for estimating storage requirements.

Table 1. Calculating database size
Database component Size
Field storage = Cust-num + Name + Start-date

= 3 + 21 + 3 

= 27
Customer table = number of records x field storage x 1.5

= 500,000 x 27 x  1.5

= 20,250,000
Name index = number of records x (7 + number of fields in index + index field storage ) x  2 

= 500,000 x (7 + 1 + 21) x 2

= 29,000,000

These formulas are conservative and often result in a large estimate of your database size.