i have the 25, and find it quite roomy. i have my wallet, changepurse, a paperback, my 60GB ipod, cell phone, a comb and i usually have a half litre pet bottle in there too, no problem. i can still fit in a light sweater or small umbrella, but then it's FULL. i think it depends on what you haul around. also, check the visual aids thread to get a good idea of how the bag looks. cheers!