Plenty of room. Able to fit a three litter hydro pack. It's comfortable easy to put on. Awesome pack.
The parcel came on time. So far, I have taken this thing on a week long trip through India, where it was strapped to the back of a motorcycle as I rode through the himalayas (I'm not kidding here). It held up great and the rainfly was very useful and easy to put over it when it poured on us. The pack endured heavy strain as it was packed to the brim and strapped down hard every day and came out without a scratch (I was surprised about that).
The product is very good,
great price (gives you more peace of mind when being rough with it)
great size, perfect for carry-on (taken on around 10+ flights, never a problem)
fairly light when empty