over all 18 inches tall, 13 inches wide and about 8 inches from front to back, thats the main section which has a 6" by 7" mesh pocket on the back side. above this mesh pocket is a headphone gland so your ipod can sit in the mesh bit and your phones come out the back of the rucksack.
the front pocket is 10" by 11" and sits very flat when empty but allows expantion up to about 2.5/3 inches, and has loads of flat pockets, a key clip and an id card pocket.
its also got a mesh pocket on left and right side measuring 6"X7",
just shout for some high detailed pics