The size is a women's XL which is the same as a mans Large (22"). As far as I know, the only difference between the women's and the men's version is the S shaped straps.

I bought this pack before my through hike last year. I took it for a 3 mile hike and determined the size was too large. MLD would not exchange it because I had tried it out. The pack has not been used since then... it is pretty much Brand New.