The first thing to consider when choosing a pack is the type of hike activity you are planning to use it for. At first glance, day packs and backpacks may look similar, but each has distinct functions and features. Also, the pack capacity you need will depend on how much gear you plan to carry. Once you’ve determined the use and capacity you’re looking for, then you can figure out the best fit.

Comfort is key. The two main considerations to comfort fit is torso length and hip sizing. Check torso fit for the pack you choose by positioning the hip belt, so the top edge is about one finger width above your hips. If there is a gap at the top of your shoulder, the pack is likely too long for your torso. The pack may be too short for your torso if the straps wrap more than a few inches down your back before they connect to the pack. As a feature, some daypacks and backpacks have an adjustable torso strap that lets you find your best fit.

How to measure the torso
Find the top of the hip bones and draw an imaginary line from top of left hip bone to top of right hip bone. On the back of the neck, find the C7 vertebrae by touching your chin to your chest and feeling for the large protruding bone at the base of your neck. Measure along the spine from the line between the hip bones to the C7 vertebrae. This is your torso length.

Hip belts accommodate many varied sizes. Just make sure you can loosen or snug up the belt to comfortably fit around you.
Sternum strap positioning should be roughly an inch below your collarbone to allow for easy arm movements.

NOTE: Overnight multi-day backpacks can come in women- and men-specific packs for better sizing. Be sure you understand all the strap features to help with proper fit. Some backpacks come with removable torso and hip belts so you can mix and match the right fit for you.