How to Fit a Backpack: Torso, Hips, and Load Lifters
Learning how to fit a backpack takes about ten minutes and fixes most shoulder pain. The order you tighten the straps matters more than how hard you pull them.
To fit a backpack, load it with 15 to 20 pounds, loosen every strap, then tighten from the hips upward. The hip belt goes on the iliac crest first, the shoulder straps second, the load lifters third, and the sternum strap last. Reversing that order is why most packs hurt.
Pack size is set by torso length, not by height. That one measurement decides more about comfort than the brand on the lid.
Quick answer
Put 15 to 20 pounds in the pack, loosen every strap, then work bottom up. Hip belt on the iliac crest first, shoulder straps second, load lifters third, sternum strap last. Most sore shoulders come from a torso setting that is too long, not from straps that are too loose.
Measure your torso, not your height
Your torso is the distance from the C7 vertebra, the bump at the base of your neck when you tip your head forward, down to the top of your iliac crest, the shelf of your hip bone. Deuter publishes that exact protocol and sizes its packs by back length in centimetres rather than by letters.
Adult torsos generally run 15 to 22 inches. Height is a poor proxy for it.
Someone 6 feet 2 with long legs can have a 19-inch torso and need a medium. Someone 5 feet 7 with a long trunk can need a large. Sizing a pack off your height is close to a coin flip.
Brands do not agree on the letters either, which is why the chart matters more than the label:
| Brand | Small | Medium or Regular | Large |
|---|---|---|---|
| Gregory | 15 to 18 in | 18 to 21 in | 21 to 24 in |
| Black Diamond | 15.5 to 17.5 in | 17.5 to 19.5 in | 19.5 to 21.5 in |
| Hyperlite Mountain Gear | 15 to 17 in | 17 to 19 in | 19 to 21 in |
| Deuter | 42 cm, women's fit | 46 cm | 50 cm |
Note that Gregory uses identical sizing across men's, women's and unisex models. A medium is a medium.
The fitting order matters more than the strap tension
Straps are a chain of dependencies. Any strap you leave tight silently decides where the pack sits, so the next strap you adjust is measured from the wrong place.
- Load the pack with 15 to 20 pounds. Switchback Travel recommends that range, and ULA Equipment suggests 10 to 20. An empty pack hangs off your shoulders and tells you nothing about how the suspension behaves under tension.
- Loosen everything. Shoulder straps, load lifters, sternum strap, hip belt, compression straps. All of it.
- Set the hip belt on the iliac crest and cinch it. The padding should wrap over the top of the bone with no gaps. This is the datum for everything that follows.
- Snug the shoulder straps. The anchor points should sit 1 to 2 inches below the tops of your shoulders. Tighten them after the belt, never before.
- Set the load lifters to roughly 45 degrees. Switchback Travel, ULA and Alpenglow Sports all cite 45. The Appalachian Mountain Club gives a 30 to 45 degree range.
- Clip the sternum strap below the collarbones and above the sternum. Snug only.
- Walk for ten minutes, then redo steps 3 through 6. Everything settles.
Osprey publishes a useful confirmation check: a correctly fitted harness terminates 2 to 3 inches beneath the armpit.
Why does my backpack hurt my shoulders?
Because the hips are not carrying the load.
The Appalachian Mountain Club states the target as roughly 80 percent on the hips, about 20 percent on the front of the shoulders, and zero on the tops of the shoulders. Switchback Travel arrives at the same 80 and 20 split independently.
When the torso setting is too long, the harness anchors above your shoulders. The hip belt then lands below the iliac crest, where there is no bone to rest on, and the load has nowhere to go but your shoulder girdle.
Here is what each symptom usually means:
| What you feel | Likely cause | The mechanism |
|---|---|---|
| Burning ache across the tops of the shoulders | Torso too long, or belt not loaded | Belt sits below the crest, so weight hangs from the trapezius |
| Visible gap between shoulders and straps | Torso too long | Straps bridge over the shoulder instead of wrapping it |
| Straps digging straight down, pack riding low | Torso too short | The yoke anchors below the shoulder, pulling vertically |
| Bruised or pinched hip points | Belt over-tightened or wrong size | Load concentrates on the bone instead of spreading across it |
| Belt slides down while walking | Belt too large | Nothing arrests it on the crest, so it walks onto soft tissue |
| Pack pulls you backward on climbs | Load lifters slack | Upper mass sits behind your centre of gravity |
| Pack sways side to side | Sternum strap unclipped or too low | The harness spreads and the load oscillates with your stride |
| Tingling or numb fingers | Sternum strap or harness too tight | Pressure over the nerve bundle at the front of the shoulder |
Two of those deserve a warning. Load lifters are a trim tab, not a lifting device. Cranking them jams the harness into the shoulder joint and pulls weight back off the hips, which produces a pack that felt fine for the first mile and awful by the second.
Where should the hip belt sit?
Centred on the iliac crest, with the padding wrapping over the top of the bone.
Osprey measures its hip belt sizes at the crest rather than at the waist, which is why a belt size rarely matches your trouser size. ULA Equipment offers a simple conversion: men add 2 inches to their trouser waist, women with curvier hips add 5 inches to their smallest waist measurement, and women with straighter hips add 3.
ULA also gives the best visual check: when the belt is closed, the two wing tips should leave a gap of 4 to 8 inches across your front. No gap means the belt is too long and the padding has wrapped past the bone.
Worth noting that not every source agrees here. Alpenglow Sports places the belt 1 to 2 inches above the crest, while Osprey, Deuter, ULA and the Appalachian Mountain Club all centre it on the bone. The majority position is the safer instruction.
How much should a backpack weigh?
The usual answer is 20 percent of your body weight. Treat it as a sanity check, not a rule.
Advnture covered the physics behind the number and found it does not hold up. Modelling by Michael O'Shea at Kansas State produces a percentage that falls as body mass rises, around 50 percent at 115 pounds down to roughly 14 percent at 240 pounds. That inverts the assumption most people carry.
There is also a floor on gear weight. A very small hiker carrying the same tent and stove as everyone else will exceed 20 percent no matter how disciplined the packing is.
Where this advice does not apply
Frameless and ultralight packs change the rules, and it is worth being clear about that rather than repeating the 80 percent line at everyone.
Writing at The Hiking Life, Cam Honan points out that webbing hip belts on frameless packs do not transfer much weight at all. Meaningful transfer needs stays running into the belt. Under about 15 pounds, many ultralight hikers deliberately run the belt loose or remove it, because the friction and weight of the belt cost more than shoulder carry does.
His threshold is useful: above roughly 11 pounds of base weight, or 20 to 22 pounds total, you want a frame.
Load lifters are the other exception. Plenty of ultralight packs do not have them, and on a pack whose frame does not rise above your shoulder there is no 45 degree geometry to create. Pulling on them just compresses the bag.
Women's-specific models are a shape claim rather than a gender one. They typically use a sharper S-curve on the shoulder straps, a narrower yoke, and a hip belt angled for a higher, more flared crest. Plenty of women prefer unisex harnesses, and men with narrow shoulders often fit women's models better.
Try the pack on loaded. Deuter's own guidance ends there, and so does ours.
For another example of how we write, see our other writing samples.
Frequently asked
- How do I measure my torso for a backpack?
- Tip your head forward and find the bony bump at the base of your neck, the C7 vertebra. Put your hands on your hips with thumbs pointing back to find the top of the iliac crest. Have someone measure the distance between the two along your spine. That number, not your height, picks your pack size.
- Where should a backpack hip belt sit?
- Centred on the iliac crest, with the padding wrapping over the top of the hip bone. Osprey, Deuter, ULA and the Appalachian Mountain Club all agree on this. The belt should close with a 4 to 8 inch gap between the wing tips across your front.
- How tight should the sternum strap be?
- Snug enough to stop the shoulder straps spreading outward, and no tighter. It sits below the collarbones and above the sternum. If you get tingling or numb fingers, it is too tight, because the strap is pressing on the nerve bundle it exists to relieve.
- Why do my shoulders hurt even though the pack fits?
- Check the hip belt before the straps. A properly loaded pack puts roughly 80 percent of the weight on the hips and none on the tops of the shoulders. If the belt is sitting below the crest, or the torso setting is too long, the shoulders end up carrying weight they were never meant to hold.
- Do load lifters need to be at 45 degrees?
- Roughly 45 is the published guidance from several manufacturers and retailers, and the Appalachian Mountain Club gives 30 to 45. It is a rule of thumb rather than a measured constant, and it only applies to packs whose frame extends above your shoulders. Snug them until the top of the pack sits close to your back, then stop.