Measuring your torso for a hiking backpack means finding the straight-line distance down your spine from the C7 vertebra at the base of your neck to the iliac-crest line at the top of your hip bones, using a flexible tape measure while standing naturally. That single number is what every backpack size chart is built around, and it takes about two minutes to find with a helper and a soft tape measure.
What is the correct way to measure torso length?
Start at the C7 vertebra. Tilt your head forward and feel along the back of your neck for the largest bony bump — it stays raised even after you lift your head back up, right where the neck meets the shoulders. That bump is the top reference point. Next, find the iliac crest. Place both hands on your waist with your thumbs pointing backward and slide them down until your thumbs catch the top ridge of your hip bones, then picture a line connecting that ridge straight across your lower back. That's the bottom reference point.
With both landmarks located, have a helper hold the end of a flexible tape measure at the C7 bump and run it straight down, following the natural curve of your spine, to the imaginary iliac-crest line. Read the number in inches or centimeters — that is your torso length, ready to compare against a brand's size chart.
What tools do you need?
A flexible cloth or vinyl tape measure is the only tool this measurement really requires, because it bends with the spine's curve the way a rigid ruler or metal tape can't. A metal tape measure will straighten the line between the two points instead of following the back's natural shape, giving a shorter, inaccurate reading. A second person to hold the tape and read the result is strongly recommended, though a large mirror can substitute in a pinch.
Can you measure your own torso without help?
Self-measuring is possible but noticeably less accurate, since holding a tape steady on the C7 vertebra with one hand while running it down your own spine with the other is awkward, and you can't see the back of your neck to confirm the starting point. If no helper is available, many outdoor gear retailers will measure torso length in-store as part of a backpack fitting, using the same C7-to-iliac-crest method, and some can do it while you try on demo packs.
What mistakes throw off the measurement?
The most common error is measuring from the top of the shoulder or the collar instead of the C7 vertebra, which inflates the number. The second is finding the waistline instead of the iliac crest — the waist sits higher than the top of the hip bones on most people, so using it shortens the reading. Slouching or arching the back while being measured also changes the spine's curve and skews the result. Standing in a relaxed, upright posture, the way you'd naturally stand while hiking, keeps the measurement consistent.
How do you read the result against a size chart?
Once you have a number in inches or centimeters, compare it directly to the specific pack's own torso-length chart rather than a generic size label, since size bands shift between brands and even between models from the same brand. A pack listing a torso range of 17–19 inches for its Medium size, for example, fits a hiker whose measured torso falls inside that exact window — not whoever wears a medium T-shirt. If the number sits right on the border between two listed sizes, an adjustable-harness pack removes the guesswork by letting the shoulder-strap yoke slide within its range.