I did a 2.5 gallon BIAB with about 5.5 lbs of grain.
Mashed and sparged in two different pots.
Mashed in 1.5 gallons (1.25 quarts/pound of grain will be 6.25 quarts for 5 lbs of grain, so just over a gallon and a half).
Sparged in 2.5 gallons.
After water loss from grain absorption and boiling...