I have no idea how to exactly do a size comparison, but let's say I bring all sorts of stuff with me. If I put all the stuff in photo 1 in the bag, I still have some room left for random stuff. Now, of course it depends how you organize the bag but I do it like this:
Photo 2
Back compartment for A4 papers
Photo 3
Laptop compartment for iPad + MacBook
Middle compartment for notebook, sunglasses and other stuff
Separate pockets in middle compartment for a) mouse, b) Duracell charger + iPod
Photo 4
Zipper compartment for cables, chargers and harddisks (including USB's)
Front pockets for a) water bottle, b) food (in this case represented by the TwelveSouth BassJump because it's rougly the same size).
I hope this helps you to get an idea of what fits inside of this bag.