Originally Posted by Yooper
Your preboil volume will be different than anybody else's volumes, as there are many factors that come into play. Relative humidity, your pot width, the strength of your boil, etc, all make a difference. Generally, you can plan on about 1 -1.5 gallons per hour with most pots and a pretty vigorous boil.
You could start with 6.25 gallons, and have some extra wort aside to add near the end of the boil if you are boiling too much off. (Add it with at least 15 minutes left, though!)
Well, my plan is to shoot for 6.5 gallons (13 for 10 gallon batches) and then check the gravity and adjust the wort accordingly with water or LME.
I'm just trying to see how I can figure out what the gravity at 6.5 gallons should be if, for instance, I am shooting for 1.048 @ 5.5 gallons.