I think the smaller one is 12oz, like the ones that they sell in the 12 packs of Dasani at the grocery. We always bring a few six packs of Dasani to keep in the room fridge but I will relent and buy one in the parks if necessary. After all of our trips we have finally in about the last year learned to go bagless and carry nothing in that can't fit in your pocket. It's a lot quicker to enter without the bag check.