Quote Originally Posted by Matt5791
One question I have is:

Say I decide that 30 seconds exposure is about right for my 5X5 print I am about to make.

Is there any calculation to enable me to decide on comparable exposure if I increase the size of the enlargement to say 8X8?
I found this chart Enlarging Ratios to be extremely useful. I believe that it is what you are looking for. I have used it myself and it works very well.

Hope that this helps,