A quick google search gave me this:
The best way to illustrate and conceptualize this in your mind is to think about a one-pound bag of DME. DME has a PPG of 44, or 44PPG. If you dissolved a one-pound bag of DME in on gallon of water it the resulting gravity would be 1.044 SG (specific gravity). Subsequently, an easier way to use this number is to ignore the gallon part of the equation. Before you add the water to your 1 pound of DME, that dry bag has 44 points in it (or 44 points per pound). Using easy math you can see that if you put that 44-point bag (one pound) in 2 gallons the 44 points would be diluted to a gravity reading of 1.022SG. Likewise, you can put that same 44 points into half a gallon and the resulting gravity would be 1.088SG (44/0.5 is 88). But the total points are always the same regardless of gravity readings. (22*2=44, 44*1=44 and 88*0.5=44)
How do we translate PPG numbers into 5-gallon batches? It may be easier if we think of recipe formulation in reverse. Lets say you want to make a 5-gallon batch of 1.044 OG. A specific gravity of 1.044 can be taken to mean 44 points per gallon. So in a 5 gallon batch there is actually 5*44=220 total points. So to make that beer you need to get 220 total points of malt in there. If you were to make it entirely using DME, which is 44PPG, then you would need 5 pounds. 220 total points divided by 44 points per pound (ignore the gallon part of PPG because you already accounted for the gallons by calculating total points). 5 pounds makes sense because if 1 pound of DME in one gallon makes a 1.044 gravity wort, then it would take 5 pounds in 5 gallons to make the same strength beer.
