Learn how to measure torso length correctly and match it to backpack size charts, so a long-torso frame actually fits and carries weight properly.
By Dana Okoro, Editorial Reviewer · Published September 14, 2026, 6:03 PM ET · Updated September 29, 2026, 6:16 PM ET
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In plain English
Your torso is the part of your back between your neck and your hips. Two people of the same height can have very different torsos, the same way two people can wear the same pants length but different shirt sizes. A backpack's frame has to match that stretch of back, or the pack sits in the wrong place.
A hiking pack is meant to rest its weight on your hips through a padded belt, a bit like a tool belt holding up heavy tools. If you have a long back and the pack is too short, the belt ends up around your belly instead of on your hip bones. Then the shoulder straps do all the work, and your shoulders tire fast.
The fix is simple. Have a friend measure your back with a soft tape, then compare the number with each brand's own size chart. Brands draw their size lines in different places, so a Large from one company may not match a Large from another. Try the pack on with some weight inside before you decide.
Torso length is the measured distance along the curve of the spine from the C7 vertebra at the base of the neck to the iliac crest at hip level, and it is the single measurement backpack manufacturers use to size a pack's frame and harness. Getting this number right matters more than height, weight, or shoe size when choosing a hiking backpack, because the frame length and shoulder-strap placement are built around it.
What is torso length, and how is it measured?
Torso length is the spine-curve distance from the C7 vertebra to the iliac crest, measured with a flexible tape and a helper, and it's the number every hiking backpack size chart is built around. It typically runs from about 15 inches on a short torso to 22 inches or more on a long one.
Finding the two landmarks takes a moment of practice:
Tilt the head forward until the C7 vertebra, the most prominent bump at the base of the neck, is visible or easy to feel.
Place both hands on the hip bones with thumbs pointing toward the spine to locate the iliac crest.
Have a helper measure along the curve of the back, not in a straight vertical line, from C7 down to the line connecting the iliac crest points.
Round to the nearest half inch, matching the precision most size charts and adjustable harnesses use.
Measuring alone with a mirror produces less reliable results than having a second person run the tape, since the C7 landmark is hard to locate by feel on your own back.
Why doesn't height determine torso length?
Height doesn't determine torso length because two hikers of the same height often split that height differently between leg length and spine length. A 6-foot hiker with proportionally long legs can have a shorter torso than a 5-foot-6 hiker built with a longer spine and shorter legs.
This is why backpack manufacturers size packs by torso length instead of overall height, and why shopping by a general "tall hiker" size guide without measuring first produces a meaningful share of poor fits. A hiker's shoe size, arm length, or general build gives no reliable clue to torso length either; the only accurate way to know is the direct C7-to-iliac-crest measurement.
How do backpack size charts use torso length?
Backpack size charts translate a measured torso length into a Small, Medium, or Large size, with each size built around a roughly 2-to-3-inch torso range and a frame or harness cut to fit that range specifically. A few brands add an Extra-Small or Extra-Large size to extend the covered range further in both directions.
A typical size structure looks like this:
Size Label
Approximate Torso Range
Typical Hiker Fit
Small
Roughly 15.5-17.5 inches
Shorter-torso hikers
Medium
Roughly 17.5-19.5 inches
Average-torso hikers
Large
Roughly 19.5-21.5 inches
Long-torso hikers
Exact cutoffs vary between manufacturers, so a hiker sitting near a boundary, at 19.5 inches for example, should check the specific size chart for the pack in question rather than assuming every brand's Large starts at the same measurement.
What if you're between two sizes?
Between-sizes advice differs by maker: Mystery Ranch recommends sizing down so the waist belt can tighten securely on the hips, while a pack with an adjustable harness may let a hiker size to the longer option and adjust down. The range an adjustable suspension covers varies by pack, so check the stated adjustment range on the size chart.
Hikers whose measurement falls well outside any stock size range, more than an inch beyond a brand's largest listed Large, are better served by a cottage manufacturer that builds frames to an exact custom measurement rather than forcing a stock size to work. Trying the pack loaded with real gear, and rechecking the fit checkpoints after walking for several minutes, remains the most reliable confirmation that a chosen size, adjusted or fixed, actually carries correctly.
Frequently Asked Questions
Have a helper run a flexible tape measure along the curve of your spine, from the C7 vertebra at the base of the neck down to an imaginary line connecting your iliac crest, the top of your hip bones. Round to the nearest half inch to match most backpack size charts.
No. Two hikers of the same height often split that height differently between leg length and spine length, so torso length can vary significantly at the same overall height. Backpack sizing always uses the direct C7-to-iliac-crest measurement rather than height.
The size table on this page is a rough, generic example rather than any brand's published chart, and brands draw their lines in different places. Granite Gear, one of the few brands in this site's source library that publishes explicit ranges, sizes Short at 15 to 18 inches, Regular at 18 to 21 inches and Long at 21 to 24 inches.3 Under that chart, a 19.5-inch torso is a Regular, while the generic table here would put it at the start of Large.
Deuter works in centimeters. It aims its regular fit at a back length of about 46 cm and its EL fit at about 50 cm, roughly 19.7 inches.6 For a long-torso hiker the lesson is to read the chart for the exact pack you want. A measurement near a boundary can land in different sizes at different brands, and one brand's largest size may simply stop short of your back.
Between sizes: the sources disagree
Some guides recommend sizing up when a long torso falls between two sizes, on the reasoning that an adjustable harness can take up the slack. Not every maker agrees. Mystery Ranch recommends sizing down between sizes so the waist belt can tighten securely on the hips.4 Mystery Ranch also measures to a different end point, a spot just behind the belly button rather than the iliac crest, so its numbers don't transfer directly to other brands' charts.4
Deuter adds a caution against leaning on adjustment: even adjustable packs should be chosen in the correct back length.6 Kelty calls a torso measurement only a starting point for fit.7 There is no universal rule here. The practical answer is to try both sizes with weight inside; Big Agnes suggests fitting a pack with 10 to 20 pounds loaded.8
How to tell a frame is too short for your back
When the frame is too short, the hip belt ends up above the iliac crest. Kelty says the middle of the belt padding should rest on the crest,7 and Gossamer Gear notes that shoulder straps set too low reduce weight transfer to the hip belt, while straps set too high pinch the neck.9 A long torso in a short pack usually shows up as a belt riding on the belly or a harness that seems to pull the pack down onto the shoulders.
That matters because the hips handle pressure better. In a lab study of load carriage, the hip region tolerated pack pressure significantly better than the shoulders, and the authors recommend shifting load to the hips wherever possible.5 How much ends up on the hips is disputed: Big Agnes aims for about 80%,8 Alpkit says 60 to 80%,10 and the US Army's foot-march manual puts it nearer 30% with a frame and hip belt.11
Load-lifter straps give a quick visual check once the belt is on the hip bones. Suggested angles range from about 45 degrees (Big Agnes) to 30 to 45 degrees (Deuter) and 25 to 45 degrees from horizontal (Alpkit).8,12,10 If the lifters run nearly flat with the belt correctly placed, the frame is likely too short for your back.
