I was just able to fit 50 pounds of uncrushed two row into 2 five gallon homer buckets. Therefore each gallon holds about 5 pounds. So, with 4 gallons you should have about 20 pounds of Marris Otter, give or take some. Hope that helps.
I have found grain to be a bit less than 1 qt per pound. I would guess 22 pounds.
wilserbrewer BIAB Bags, Hop Bags and Ratchet Pulleys for sale
Expert tailor and supplier of custom sized, top quality BIAB bags, hop bags and ratchet pulleys at reasonable pricing http://biabbags.webs.com