I just checked on my G4 pack by going on line and looking at my order history from Gossimer Gear.
The pack I have is a medium for a 19 inch torso (as per the site sizing chart) with a large belt.
MML--The Man, The Myth, and the Legend
"I am the eagle, I live in high country, in rocky cathedrals that reach to the sky;
I am the hawk and there's blood on my feathers, but time is still turning they soon will be dry;
All those who see me, and all who believe in me, share in the freedom I feel when I fly.”