Originally Posted by ajf
When Jamil gets a bit more experience, he will find that he doesn't really need to make a 6g batch to end up with 5g in keg or bottles.
I usually go with 5.5 in the fermenter, and get pretty close to 5 gallons in the keg. I've been trying to increase my recipes slightly to get a full 5 gallons in the keg, but I usually forget until about 1/2 through the boil.
If you have a 6 gallon carboy, you aren't going to want to put more than 5, 5.25 gallons in there. If you have a 6.5 gallon carboy, 6 gallons is a tight fit. I guess that sounds like a silly way to determine what size batch you want to make, but it really isn't. Consider your fermenter size when deciding how much wort you want to put in there. (Some of these things I had to learn the hard way!)