Torso length for a backpack is measured from the C7 vertebra at the base of the neck to the iliac-crest line at the top of the hip bones, using a flexible tape measure held straight down the spine. This single number, not your height, determines which frame size fits a short torso correctly.
How do you measure torso length for a backpack?
Tilt your head forward until you feel a bony bump at the base of your neck — that's the C7 vertebra, and it's the top reference point. Place your hands on your waist with thumbs pointing backward until you feel the top ridge of your hip bones, then draw an imaginary line connecting that ridge across your lower back — that's the iliac crest, the bottom reference point. Have a helper run a flexible tape measure down your spine from the C7 bump to the iliac-crest line, following the curve of your back rather than a straight vertical line. The result is your torso length in inches or centimeters, ready to compare against a brand's size chart.
What tools do you need to measure torso length?
A flexible cloth or vinyl tape measure works best because it follows the curve of the spine; a rigid tape measure will give an inaccurate, straightened-out number. A second person to hold the tape and read the measurement improves accuracy, since it's difficult to locate your own C7 vertebra and hold a tape steady at the same time. Wearing a fitted shirt, rather than a bulky jacket, makes both landmarks easier to feel and measure.
- Flexible tape measure: follows the spine's curve for an accurate reading.
- A helper: locates landmarks and reads the tape while you stand naturally.
- A fitted top: removes bulk that hides the C7 bump and hip-bone ridge.
- A pen or marker: optional, to mark the two points before measuring if you're working alone.
What if you're between two sizes?
When a measurement falls between two size bands — for example 16.5 inches between a brand's XS and Small — sizing down generally works better for a genuinely short torso, since an oversized frame lets the hipbelt sit too low and the shoulder straps ride the load onto the neck. Packs with an adjustable harness remove the guesswork for a between-sizes measurement, since the back panel can be fine-tuned by half-inch or centimeter increments rather than forcing a choice between two fixed sizes. When only fixed sizes are available and the pack will carry heavier loads, sizing toward the smaller option and testing hipbelt position with a loaded pack is more reliable than guessing from the number alone.
How does torso length compare to pack frame size?
A pack's stated frame size (XS, S, M, L) refers to its internal suspension length, which should sit within a few centimeters of the hiker's own torso length for the hipbelt to land correctly on the hip bones. Frame size is distinct from pack capacity in liters — a short-torso hiker can still carry a large-capacity pack, as long as it's built or adjusted to a short frame length, since capacity and suspension length are set independently by most manufacturers.
What mistakes throw off a torso-length measurement?
The most common mistake is measuring straight down the back with a rigid ruler instead of following the spine's natural curve with a flexible tape, which shortens the reading and can push a hiker into a size too small for their actual shape. Slouching or standing unnaturally straight during the measurement also skews the number, since the goal is a relaxed, natural standing posture rather than a stretched or hunched one. Measuring over a bulky jacket instead of a fitted shirt can hide the iliac-crest ridge, leading to a hip-bone reference point that's too low and a torso length that reads longer than it actually is. Re-measuring on a different day, or having a second helper confirm the reading, catches most of these errors before they turn into a poorly fitted pack.
Should you remeasure over time?
Torso length in adults stays fairly stable, so a single accurate measurement usually holds for years, but it's worth remeasuring after a significant change in body composition or before buying a first backpacking pack if the last measurement was taken casually rather than with a tape and a helper. Growing kids and teens should be remeasured before each new pack purchase, since torso length changes quickly during growth spurts and a pack sized to last year's measurement can already be too long by the time it's used again.