When trying on alpine touring boots, take the liners out of both boots and slide your bare feet into the shells. Move your feet so that your toes are touching the inside front of the boot, but not smashed against the front. Stand up in the shells and the space between the heel of the boot and your heel should be the width of 1-2 fingers. More then two fingers and the boot is too big, less and the boot is too small (unless you know you want and very snug fit). Next, put the liners back in the boot and try boots on with the socks in which you’ll be skiing (which should be a thin wool sock) Quick side note on socks, all companies have included warmth as an R&D objective in designing liners. Having a thick sock will likely make the fit of a boot too tight, restricting circulation and ultimately leaving your feet feeling colder. Back to the boots, once you have the boot on it should feel at least a little snug. This is the tightest the boot is going to feel since from here you will be heat molding or breaking in on the hill. So if it feels loose when first trying it on, as you break it in it will likely be too big.
Boots only come in full shell sizes: At CCBC we only buy boots by the full shell size to not confuse the issue, but it is important to note that even though the boot says 27.5 on the box it is the exact same as 27.0. This is true for all brands except Scarpa, that for some reason breaks on the half size. Therefore with a Scarpa a 26.5 it will be the same as a 27.0.
Heat Moldable Liners: Make sure you buy a boot with a heat moldable liner(most all AT boots come with a heat moldable liner). Even though half sizes are a myth you can more than make up for being in between with a good heat mold. These liners are way improved from where they were years ago. They can take multiple molds and will last way longer before needing to be replaced.
A boot “last”: The last refers to the widest part of a boot, the forefoot. 100mm tends to be the standard, a wide last will be around 102 and a narrow last will be around a 98.
Blisters: Your feet are carrying extra weight, sweating and moving against a hard plastic boot so sometimes you’ll get blisters. The lighter and better fitting the boots, the less likely blisters are. Pre-taping your feet with duct tape seems to be the easiest solution for blisters.