One of the keys to a comfortable backpack is to get a pack that is the right size (e.g., small, medium, large) for you. Your torso length—not your height—is the key measurement; hip size can also be helpful.

The pack-fitters at your local REI store are your best resource to get the right size pack. This article gives you the basics for shopping online.

Find Your Torso Length

Torso length

To do so, you'll need a friend and a flexible tape measure.

  • Have your friend locate the bony bump at the base of your neck, where the slope of your shoulder meets your neck. This is your 7th cervical (or C7) vertebra. Tilt your head forward to locate it more easily. This is the top of your torso length.
  • Place your hands on top of your hip bones (also known as your iliac crest), with fingers pointing forward, thumbs in back. This is the "shelf" on which your pack will rest. The middle of an imaginary line drawn between your thumbs is the bottom of your torso length.
  • Using the tape measure, your friend should measure the distance between the C7 and the imaginary line between your thumbs. Be sure you stand up straight when being measured. You now should have your torso length.

Use your torso length measurement to find your best pack size. Generally, manufacturers size their pack frames something like this:

  • Extra Small: Fits torsos up to 15 ½"
  • Small: Fits torsos 16" to 17½"
  • Medium/Regular: Fits torsos 18" to 19½"
  • Large/Tall: Fits torsos 20" and up

On REI.com's product pages, you can find the torso range for each pack size listed under the "Specs" tab. If your measurement is right on the border (say, 17¾"), it's best to visit an REI store to try on both sizes of that pack.

REI typically carries adult packs sized to fit torso lengths as compact as 12" (10" for children) and as long as 23". If your measurement lies outside that range, you might require a custom-built pack.

Determine Your Hip Size

While less important than torso length, your hip measurement is useful to know. It's especially helpful if you are considering a pack that offers interchangeable hipbelts.

Take your tape measure and wrap it around the top of your hips. The correct measurement is along the "latitude line" that radiates out from your belly button to your sides and the high points of your hip bones. This is slightly higher than your waist, so your hipbelt measurement may differ from your pants waist size.

A properly positioned hipbelt will straddle your hips about an inch above and below that latitude line, wrapping around the 2 pointy pelvic bones on the front of your body.

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Torso length illustration courtesy of Gregory Packs.