[Zope] pointers on predicting ZODB size based on size of files to be imported?

Hi Is there any documentation anywhere or advice on being able to estimate the size of a potential Zope ZODB instance based on the size of a current site? For example if you were to have a site of say 5 gb consisting of HTML pages, graphics, images, pdfs, word docs, excel files etc : are there any pointers anywhere on roughly how many gigs of ZODB this would take up? Obviously word, excel and other binary formats will likely translate to more weight... Also are there any ZODB growth prediction charts at all? -- michael