When ordering online, there are a few tricks to getting the right size boot the first time. Start off by using the manufacturer's sizing guide. Most boots allow room for the hiking socks you'll be wearing but do check out any notes or reviews on how they size up in real life, as some come out smaller or larger in practice (the boots we tested here sized up true unless otherwise stated). Most retailers will take returns so long as the boot hasn't been worn outside. If you're trying a boot on, do it at the end of the day when you're feet are already tired and naturally a little swollen from use, as that will give you a better indication of fit after a long day on the trails.
You're looking for a fit that's snug but not tight, supportive around the mid-foot, with no obvious pinching or rubbing. When walking on the flat, climbing and descending, your heel should stay in place and not move up and down inside the boot, as that could lead to blisters. The toes should have a little wiggle room, but not enough that the foot moves around within the boot. Once you've found the perfect pair, head to our guide on how to break in hiking boots and, of course, how to care for hiking boots, so they last for years.