"That depends on a lot of things
percentage alcohol in wash, how much and when you take of tails and heads, percentage of final output.

but you could estimate
5 gal of wash at 15% ABV is 3/4 gallon of 100% collectable at 100% distilate (which as you know is not possible - more likely about 85-90% ABV)
or figure it in ounces = 96 oz of pure - but you won't get all of it anyway - maybe 60-80 oz

by the time you lose the heads and tails, probally 60 oz at 90%.

cutting it to 80 proof gives you just over double that. maybe 110 oz?
110 oz is 3.2 liters
if you can get 130 oz you end up with 3.8 liters

anyway, that's the math to the best of my ability, just do the actual, see how close you get. good luck"