Hi,

I would like to add that the database size should be multiplied by 5:

First, some people tend to create a an extra database on the same machine to QA something before the upgrade so the QA test would go not in the similar environment (this is a must) but also in a real environment.

And the other 3 times the database size is for the 3 days worth of the maintenance plan backups. It is true that we need 2 days most before the thing goes to the tape or SAN, but I had multiple cases when developers or sysadmins during the upgrade or update would backup the database in between planned backups and then the next planned backup finds itself short on space.