Leave enough room at the end of the boot
Just like when you used to get new shoes, leave enough room at the end of the boot. This is particularly important with hiking boots because when walking up or downhill, your feet will need room to move depending on the angle of your feet.
A finger’s width is a decent amount of room to leave, and if you’re unsure about how much room there is, take out the insole and check it against your feet.
Lace them up properly
If the boots aren’t properly laced up then you won’t get an accurate feel for how well they fit. Make sure the tongue is central and firmly lace the boots up, using all the eyelets. However, be careful not to lace them too tight or the boots will be uncomfortable.
Take a walk in them
If you really want to know what the boots feel like, then have a walk around in them. If possible, try and walk on different gradients to see how your feet feel in them going uphill and downhill.
If that’s not really possible, then move your feet around in the boots. Push your feet forward to see how much room there is. Then, squat down to ensure your heels don’t rise up too much. Roll your feet slightly from side-to-side to check there is enough support.