How big are your dogs?
General rule of thumb: get a boot that is one size bigger than your shoe size. It's a better idea to wear one thicker pair of socks rather than layers of thinner socks. Your feet will breath better and be warmer (and your feet won't stink as much). With your snowboarding socks on, you will want your toes to not be all bunched up in your boot and you definetly don't want your foot to be sliding around in there. Your heel needs to be planted solidly in the back. If your boots are slightly snug at first it's okay, the boot liner will compress with wear.

For Juniors
For your benefit, we locked a guy up for a week to crank out this chart. Appreciate it.