How Ski Boot Last Changes with Size

Ski boots come in widths, referred to as "last" which is referring to the measurement of widest part of the boot internally without the liner.  A standard Mid Volume or MV last is 100 mm, but they are not 100 mm in every size.  That published last width of 100 mm is only applicable at 26.5.  As you increase or decrease a shell size the width of the boot also changes by 2 mm. So in a 29.5 a 100 mm last would actually measure 106 mm, and in a 24.5 96 mm.

If you measure 106 mm in width at 29.5 your feet are not wide. If you measure 96 mm in width at 24.5 you’re not narrow. Proportionately they are the same as measuring 100 mm wide at 26.5. 

For people with wider feet, knowing how wide their feet are and doing the math for their respective size. It is common for ski boots to be narrower than your feet are especially as feet get wider or higher volume, but in most cases wider feet are squishier. They can handle more compression than a narrow rigid foot -- so don't be alarmed. Boots can also be stretched if need be. When you are shopping for ski boots you want to find a boot that feels like an extension of you while feeling secure and stable. That's what the end goal is when you're having custom boot work done, so pick a better starting point and you'll be much happier with the fit of your boots.