I was reading about BM's OktoberFAST recipe, and would like to scale it down to a 5 gal. batch size.
Someone once mentioned online calculators being good at this task.
You are looking at the hole in the doughnut and not the doughnut itself.
You primates are so predictable.
I don't know about online calculators, but if you have Java installed, you should be able to use Strangebrew Java, a quite good and free brewing application for all platforms supported by Java.