To paraphrase Johnnie Cochran, "If the boot don't fit, you might as well quit." Skiing, that is. Your ski boot is the single most crucial component of your gear system. It is steering linkage and suspension rolled into one. If your boot is too big, too small or too stiff, the connection to your ski will be compromised.
Unfortunately, buying ski boots is a process that can take hours, if not days. You've probably spent an hour selecting a pair of cross-trainers¿and they're made from soft materials. A rigid plastic boot shell will never conform to your foot's subtle nuances, no matter how long you wear it, so it's worth investing the time to find a good fit.
Most shops carry only four brands, so visit more than one if possible. City shops are least busy midweek and at odd hours, especially before ski season. Resort shops are jammed at the beginning and end of the day, so be prepared to trade skiing time for personal attention and go when everyone else is on the hill.
In the shop, try all brands, in different models and sizes. When you find a "winner," make sure it fits both feet well, then keep one on to compare to other models/brands.
Your feet can swell by as much as a half-size during skiing, so try to shop in late afternoon or evening¿or after exercise¿when your feet are their biggest.
Don't buy a boot that is too big because it feels comfy in the shop. A good-fitting boot actually feels tight out of the box and may remain quite snug during the first few days of skiing. Relax. Your liner will. Oversized boots can cause pain and fatigue, even worsen your skiing. Your feet will "swim," and you'll find yourself in the "backseat," clawing with your toes and overworking your thigh muscles to maintain stability.
When you think you've found a good fit, keep it on and walk around the shop for 10 or 15 minutes. Flex repeatedly to seat the foot and start the foams compressing. Only then can you even begin to feel what the boot's eventual fit will be.
Shell fit is paramount. Liners can easily be shimmed, trimmed or stretched, but shell work is best kept to a minimum. To check shell fit, remove the liner and put your foot in the shell. Slide your foot forward until your big toe touches the front. A finger to a finger-and-a-half of space between your heel and the shell will give you a good snug fit when the liner is reinserted, assuming no other parts of your foot are touching the shell. Anywhere you feel contact is a potential "hot spot." Be aware that if a boot has a good shell fit, but feels tight with the liner reinserted, it may be a "short-lasted" liner, which a bootfitter can stretch.
Pay close attention to the fit of the cuff, the boot's most critical power-transmission zone. You'll ski better in a boot that contours snugly along your lower leg with the buckles set somewhere near the beginning or middle of their ladders.
Just as important as leg contact is the angle of the cuff in relation to your shin bones. If you're knock-kneed or bowlegged, the top of the cuff must be angled inward or outward, respectively, or your skis won't sit flat on the snow. Look for a good cuff-angle adjustment, or ask the shop person to demonstrate it. Three out of four skiers would benefit from realignment.
Cuff height also dramatically affects stance. Short skiers might have difficulty balancing in boots with tall cuffs, as might bowlegged or knock-kneed skiers. If you're having stance problems, try models with lower cuffs. A good boot-fitter will be able to spot balance problems.
Use stamped sizes only as a guideline. The sole lengths and inner cavities of supposedly similarly sized models can vary significantly. Instead, use sole lengths, which are embossed on the outside of the heel on all shells.
Liner construction and materials also affect fit. A Racer model might feel tighter than the same manufacturer's Freerider model.