Projected OG

[Brews and Blues]

I'm working on a my first non-kit recipe here. Sticking with extract brewing, I am going to do a super simple SMASH beer just for the sake of learning some hops and extract flavors. (I know not all extracts are SM, but I still consider it a learning experience.)
Now, DME is 42 PPG. I am going to use 6lbs of DME.
Mass of extract x PPG = GP x volume of wort
So....

6lb x 42PPG = GP x volume of wort.

For volume of wort, am I using the amount of water that i am starting with, presumably 6 gallons? Or should I use the 5 gallons for the batch size i am hoping to end up with?
Or, do I find a OG that I am shooting for and use the hydrometer to take readings as I add water to the wort after boiling?

 

[RM-MN]

Your OG is defined as the gravity of the wort going into the fermenter. Before boiling is called preboil gravity.

With extract you know the amount of sugars so you calculate what the OG should be at the 5.5 gallons you put into the fermenter. The .5 gallons is to account for the trub left when you bottle.

 

[Brews and Blues]

Your OG is defined as the gravity of the wort going into the fermenter. Before boiling is called preboil gravity.

With extract you know the amount of sugars so you calculate what the OG should be at the 5.5 gallons you put into the fermenter. The .5 gallons is to account for the trub left when you bottle.

Thanks!