I myself glue: INSIDE. - Large double zip main compartment with removable dividers. L 26cm, H 19cm, 15cm P (about) + 2 large independent compartments (one on each side with "scratch") + zipped net over the entire flap (large capacity).
OUTSIDE. L 50cm, H 25cm, 25cm P (about and overall in charge) - 2 size Honourable front pockets + 2 large pockets (with "scratch") on one side pocket relatively flat across the back length (without closing).
As for me, I easily accommodates a Nikon d90 and d5100 with grip and lens attached (18-200 and 70-300) down 35 small heads + f / 1.8 + flash + 700 connections, battery and charger, maps, leaflet, papers, maps and touring various small equipment ... but we can do less.
What more? : Shoulder strap with reinforcement XXL comfortable and everything ... robust and discreet; quality / outstanding price!