densitometer question

I am using a nikon 9000 and silverfast Ai for scans, and in the process have decided to use a different regimen in my black and white photography, so I am testing film and developer.
One needs to get certain densities in a b/w neg to get filmbase +fog to yield Zone I, ie 0.08 to 0.10 negative density.
Silverfast uses the range of 0 to 220, and I do not know how to conver this to common log density figures.
Anybody know this??

I should have stated that Silverfast has a densitometer function in its program. That is what I am using to scan negatives. Hope that is clear.