Gossamer Gear G4-20 Ultralight 42 Backpack

Torso length:
Start at the C7 vertebra at the base of your neck. The best way to find this is to bend your neck and feel the first bump along the base of your neck. This bump is where you will want to start your measurement.
Next, you’ll want to find the midpoint between your iliac crest. To find your iliac crest, cup your hipbones on both sides and find the center point on your spine. This midpoint is where your thumbs should be pointing.
Finally, you’ll need help measuring from the C7 vertebra to your iliac crest. From there, you’ll have your torso measurement.

If you’re in between sizes, you will want to
+ Size down for more of a shoulder wrap and higher hipbelt
+ Size up for a lower hipbelt fit

Hip Measurement: 
You will want to find your iliac crest again by cupping your hipbones on both sides. Then, wrap a soft measuring tape or string around the top of your iliac crest. This will tell you your hip measurement.

Small:
Torso – 11.5″ – 15.5″
Hip – 25″ – 35″

Medium:
Torso – 15.5″ – 19.5″
Hip –  30″ – 42″

Large:
Torso – 19.5″ – 23.5″
Hip – 32″ – 50″