Length:
A good check for length is to slide your foot forward in the unlaced boot until the your toes hit the front. You should be able to put one finger behind your heal. If you can’t fit a finger it is too small if you can get two fingers it is too big.
Check both feet because one foot should be bigger then the other.
Slipping
On a flat surface your boot shouldn’t slip more then a quarter inch (half the width of your pinky finger). Any more slippage then a 1/4 inch and you have a good chance of getting a blister. Also a stiffer boot will take time to break-in or soften up, so initally they might slip more then 1/4 inch.
Overall
You want a snug fit with no pressure points. A loose fit will cause blisters. Your feet will swell some and they will lengthen a bit. The amount depends on the person. Do your feet swell if you have been on them all day or after a hike or run? Maybe try the shoes on with a thicker pair of socks then you will normally use. My feet didn’t swell much during my hike and the lengthened maybe a half size. A friend of mine had really hard time because his feet lengthen 2 sizes from a 9 - 11. There isn’t much you can do at the begining of your hike to plan for this. Other then actually hiking for a few weeks.
It’s a fine line between loose, snug and tight. Don’t be concerned with boot size as much as how they feel. Sizes will vary between brands. So my advice it to get a good fit with alittle room for swelling.
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