DB size formula

Ok.. I know there is one floating around here :) Does anyone have a formula for figuring database sizes and growth in order to help predict system storage requirements. Here are the variables that I know:

# of fields in DB
characters in each field
additions to DB/ day

Any help would be appreciated.
Chris

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                                                  ____       _
    Chris Duncan                               | __\_\_o____/_|
    ITS Customer Services B211                 <[___\_\_-----<
    duncanc_at_osshe.edu                          |  o'
	737-6927
                  The secret of the universe is _at_*&^^^ NO CARRIER