1.75 gallon keg that is 11 inches tall and would easily fit in most fridges. Add a paintball tank, a regulator made for one and a cobra tap and you're good to go. The paintball tank and regulator can still be used if you eve get a dedicated fridge for kegs. I use mine for my portable setup as well as for force carbing. I always keep 2 full paintball co2 tanks at all times. 5# tanks of co2 can't be filled at night or on weekends, paintball tanks can always be filled at night and on weekends, they make a great backup.