My Son, who likes math (must be adopted..
) figured this out. He says 100 pounds of raw tomatoes (before processing through tomato mill) equaled 6 gallons of raw sauce. Cooking down the raw sauce by 1/2 total volume (this would produce a thick sauce) netted 3 gallons of finished sauce, ready to can. He says he has done three batches and all were almost exactly alike as to weight and volume.
So 4 quarts equals a gallon and that would mean 12 quarts of plain sauce ready to can. He used only paste/drying varieties of tomatoes which translates to much less water content so I would imagine if someone was using any old tomato, it might effect the pounds to gallons finished rate? ( I SUCK at math...) Or would it not change the ration but require more cooking down time?
This is helpful to me because I keep detailed records of total weight of tomatoes picked from each plant so I think I can now look at my notes and figure out more accurately how many plants I need to plant to get my 100 lbs.