Depending where you live be carefull where you get measureared for a pack as well. My son lives close to a Chicagoland REI. I told him to go there and get measured so I could make him a G4 improved! He went a week or so ago and they said wait a bit there is only one person that works here that knows how! The girl that suposedly could read a tape measured him and said his torso was 16 inches and he needs a small! He is 5 11 like me and built like me. I said no way have Mom Measure you :she is radiologost tech knows her bones! So next timehe is out we do. His torso is 19 and a half like me! I know of no small pack that fits 19 and half inch torso! This is pityfull coming from a REI store. I told him he should write a letter to REI corp!