this might help: dont worry about brand, check the shell fit:
So you want to buy some new boots? This information applies to All double boots (boots with removable liners): downhill, telemark, alpine touring, snowboard, ice climbing, and any ability or age.
First of all the sizing information on the tags is not always accurate. Different brands fit differently and sometimes the sizing tags on the boot are gone. If it is right type of boot, in the right price range, and about the right size, try it on. The first step is to shell fit. With the liner removed, your foot in the shell only, and your toes touching the front of the boot, you should have NO MORE then 2 fingers, 2 cm or ¾ inch between your heel and the back of the boot. You also want about 1-3mm around the width of your foot. Yes they will feel a bit snug at first, but they will pack out.
Put the liner back in and lace or buckle the boot up and make sure that your heel is back all the way in the boot. Then when you flex the boot forward, your heel should stay down, your toes should come back from the front of the boot, and they should feel comfortably snug. Keep in mind that they will stretch out ¼ to ½ size as your foot works it way back in in the boot, and the liner packs out and molds to your foot.
If you go bigger then this your foot will slide around, and cause blisters, you will have to over tighten your boot to make the foot stay in place, cutting off the blood flow and making your feet colder. Boot fitters can make a small boot bigger, but can not make a big boot smaller.