sg and fg

hey guys whats up?
I buy my beer kits from williams brewery(great company).
I use ther red ale kit which comes with 7lbs. malt, hops and liquid yeast.
I now harvest my own yeast from previous batches. which means I will be buying malt and hops seperate from a kit.Heres my question.most malts come in 6 or 8lbs.whats the protacol an extra pound of extract?should i still brew 5 gal or go to 6 gal.how do i determine the new starting gravity and will the fg be different from the 8 lb mix?

Dry Malt Extract (DME) gives about 46 gravity points per pound per gallon of water. That means one pound of DME in one gallon of water has a gravity of 1.046. Liquid Malt Extract (LME) give about 35 gravity points per pound per gallon.

If you run the numbers, a pound of DME in 5 gallons will give you 9.2 gravity points. A pound of LME will give you 7 points in the same 5 gallons.

Your best bet is to use DME. It's a much more consistent product and stores very nicely, so you don't have to use the whole bag. Just store the excess in a zip lock bag in the refrigerator.

Prosit!