Quote:
Originally Posted by skinnyterror
Hypothetical question here...
I've calculated my grain bill using a 68% efficiency and a gravity reading of 60gu's. Let say that my efficiency ends up being 75% and my new gu reading is around 67. So in order to get down to 60 gu's I need to add about 1/2 gallon of water. I plan on using a wyeast packet to ferment my beer and the packet states that there is enough yeast for a 5 gallon batch. Will this be enough yeast if I end up with more beer due to a higher efficiency?

Why not just make a bigger beer with 5 gallons? The convention is to call the gravity reading Original Gravity (OG).
Gravity Units could be mistaken for the gravity points per pound per gallon (PPG). For instance, DME yields 45 PPG so you should get 45 gravity points for every pound of DME per gallon. 10 pounds of DME would be 450 points divided by 5 gallons = 1.090 OG
If you add up all your gravity points and have a desired OG, you can solve for post boil volume.