Your torso length — not your height — determines pack size. Measure from the C7 vertebra at the base of your neck to the iliac crest at the top of your hip bone. A partner with a flexible tape measure makes this accurate. The resulting number places you in the sizing chart below, but always check the brand’s own specs; sizes vary. Once you have the right pack, the adjustment sequence matters more than most hikers realize.
Measure Your Torso for Pack Size
Tilt your head forward to find the bony knob at the base of your neck — that’s C7. Place your hands on your hips so your thumbs point backward; the top of your thumb lands near the iliac crest. Measure the distance between those two points along your spine. Match that number to a pack size. A 16-inch torso fits a small; 18 inches takes a medium; 20-plus inches needs a large. Most weekend trips call for a 45-to-50-liter pack, while week-long treks push into the 50-to-70-liter range.
| Torso Length | Pack Size | Trip Volume |
|---|---|---|
| 15–15.5 in | XS | 45–50 L (1–2 nights) |
| 16–17.5 in | S | 45–50 L (1–2 nights) |
| 18–19.5 in | M | 50–70 L (3–7 nights) |
| 20+ in | L | 70+ L (week-long/winter) |
The Adjustment Order That Transfers Weight
Loosen every strap — hip belt, shoulder straps, load lifters, sternum strap — before putting the pack on. Load it with 10 to 15 pounds to simulate real weight. Then follow this sequence exactly.
Waist belt first. Position the padding so the iliac crest sits in its center and the belt wraps 1 to 2 inches above the hip bone. Tighten until snug but not restrictive. The padded section must cover both hip bones completely with no gaps. If it sits on your stomach instead of your hips, it will compress your diaphragm and restrict breathing.
Shoulder straps second. Pull them down and back so they wrap closely around your shoulders. The attachment point should sit 1 to 2 inches below the top of each shoulder. Straps must lie flat — no bunching, no gaping, no pressure against the neck.
Load lifter straps third. These small straps sit on top of the shoulder pads. Tighten them until they pull the pack closer to your back at roughly a 45-degree angle. A slack load lifter lets the pack fall away from your body, raising the center of gravity and increasing fatigue.
Sternum strap last. Connect the shoulder straps across your chest, 1 inch below the collarbone or across the middle of the sternum. This eliminates side-to-side sway and relieves pressure on your shoulder joints. It should not limit breathing or arm movement.
If your pack has hip belt stabilizers, snug those for comfort after the main adjustments are set. This sequence works for most US-standard backpacking packs; European brands sometimes use centimeters for sizing. For a deeper look at small gear that makes your setup more comfortable, see our roundup of tested backpacking accessories.
Common Fitting Mistakes
Three problems cause most of the discomfort. First, the hip belt rides too low or sits on the stomach, which shifts all load to the shoulders and strains the neck and lower back. Second, the load lifters stay loose, letting the pack sag backward and forcing the shoulder straps to overcompensate. Third, gaps between the waist belt and your body create pressure points — the belt must rest flush. Check for respiratory restriction after cinching everything: you should be able to take a full breath without the belt or sternum strap fighting your chest expansion.
FAQs
Should I size a backpack by height or torso length?
Torso length is the only reliable measurement. Two people of the same height can have completely different torso-to-leg proportions, and a pack sized by height alone will sit wrong on both.
How tight should the hip belt be?
Snug enough that you feel the weight lift off your shoulders when you tighten it, but not so tight that it restricts breathing or digs in. The padding should cover the hip bones with no gaps. If the belt slips down after a few minutes, it is too loose.
Does the adjustment order matter if I already own the pack?
Yes. Setting the hip belt before the shoulder straps is the single most common sequence mistake. If you tighten the shoulder straps first, you shift weight onto your shoulders before the belt can do its job, and the pack never rides correctly no matter how much you adjust afterward.
References & Sources
- Appalachian Mountain Club. “Carry in Comfort: How to Fit a Backpack.” Covers the 80/20 weight distribution rule and strap alignment sequence.
- The North Face. “How to Fit and Wear a Backpack for Comfort.” Details load lifter angle, center-of-gravity benefit, and weight placement.