Your torso length, not your height, determines your pack size. To measure your torso length have a friend use a flexible tape measure.
Start at the 7th vertebra – it is the bony bump at the base of your neck, where your shoulder meets your neck. Measure down to the top of your hip shelf. To determine the top of your hip shelf place your hands on your hips so you can feel your iliac crest. The iliac crest are the twin pointy protrusions on the front of your hips. Position your hands so your thumbs are reaching behind you, and pointing toward each other.
Your torso length is the distance between the 7th vertebra, and the imaginary line between your two thumbs.
Measure your waist around the top of your hip bones.
Pack Position On Your Body
With a slightly loaded pack on(10-15lbs), the top edge of the waistbelt should ride about 1″ above the top of your hip bones. Try lifting your leg so that your thigh is horizontal with the ground. The break in your leg should be level with the bottom of the waistbelt. If your leg pushes up on the waistbelt when you lift it, re-position the pack higher on your hips. A common mistake is made by positioning the pack to low.
Sternum Strap Adjustment
The sternum strap may be moved up or down on the shoulder harness. It should be positioned so that it is comfortable, and does not restrict breathing.
Shoulder straps and load lifters should be positioned so that the load lifter straps are tight, and are at 45 degree angle from level.
Distributing You Packs Weight
With a few quick adjustments you can shift the weight entirely onto your hips, or entirely onto your shoulders – or distribute it between the two. This allows you to relax or stress different parts of your body while in motion. Experiment on the trail to find the optimum adjustment for various terrains and activities.