They sell both sizes separately if you want to pick up a spare bottle that is a different size from what comes with the gun you order. The gun I have is a 1/2 gallon and that works out well for what I use it for. The smaller size is probably easier to handle, but even though I bought a smaller bottle for it last year I haven't bothered using it yet. My guess is that 75 -90% of the foam gun users here have the smaller bottle so it must work out pretty well for them. I guess I'm used to the mix I make for the 1/2 gallon size and I never seem to have a problem finding a use for all of the foam.