Weight & Torso Length

What is missing when you fit a pack on the sales floor, or design a pack? Where exactly does the length of your back compare to the measurements of the pack? When does a comfortable fit matter the most? Children are estimated to be vulnerable to back/shoulder problems whenever the weight of the pack exceeds 12.5% of their body weight. I would agree that the average adult would have this issue as well. So, once the weight you carry exceeds 12.5% of your body weight, you should consider a waist belt that allows for the transfer of weight from the shoulders to the hips. And, at this point torso length and pack height become very important. As well as potential variables in wearing the pack; above the hips, on the hip bone, or below the hip bone (1,2,3 inch variances). Here is how a few different pack designers/retailers/manufacturers figure the fit of their pack designs.
http://www.mchalepacks.com/packs/detail/measure.htm Torso length or back length, measured from the 7th cervical (bump on back of neck) to the Pelvis. The point at which you measure the the pelvis is important. The iliac crest can vary 2" depending on where you measure it, and certainly how you wear your pack can effect your fit. Measure to the floor on from both points and subtract the two for best accuracy.
http://mysteryranch.com/packs/sizing.php Yoke and Waist belt sizes. All Packs come with adjustable yoke instead of back length.
http://www.cilogear.com/fitandsizing.html .....Small fits from 14.5 to 17.5 inches Medium fits from 17 to 19 inches Large fits from 19 to 22 inches .... Small / Medium fits from 14 to 17 inches Medium / Large fits from 17 to 21 inches
http://www.rei.com/expertadvice/articles/backpacks+adjusting+fit.html Extra Small: Fits torsos up to 15-1/2", Small: Fits torsos 16" to 17-1/2", Medium/Regular: Fits torsos 18" to 19-1/2", Large/Tall: Fits torsos 20" and up
http://www.gregorypacks.com/us/index.php/Gregory/Pack-Fit/packfit.html http://www.gregorypacks.com/us/files/fit_guide.pdf X small 14" - 16", Small 16" - 18", Medium 18"- 20", Large 20" - 22"
http://www.ospreypacks.com/PackTech/SizingandFitting/ X small 16", Small is 16" - 18.5", Medium 18" - 20.5", Large 20" - 22.5", X large 22"
http://www.arcteryx.com/pack-fit-guide.aspx http://www.arcteryx.com/pdf/S08-Sizing-Charts_Packs.pdf Larger Volume Packs are 4 inches per size; Small 16" - 19", Medium 18" to 21" and Large 20" to 23"..... Smaller Volume Packs Regular 16" to 20", Tall 19" to 23"..... Women's Specific, Small is 14" to 17", Medium is 16" to 19" and Large is 18" to 21". Larger ranges per size are most likely due to adjustable harnesses & designs.
http://www.mec.ca/Main/content_text.jsp?rnav=info&FOLDER%3C%3Efolder_id=2534374302881817&CONTENT%3C%3Ecnt_id=10134198673221183&bmUID=1214824380415
Short (16" to 19") 41-49 cm, Standard (18" to 20") 46-53 cm, Long (20" to 23") 51-59 cm
http://www.thenorthface.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10051&storeId=201&productId=29011&langId=-1