The bottom ones holds the complete bag of large dog food from petsmart- Don't really understand the needs for the top on as it is a headache to remove the top one to get food from the bottom and I see no point in splitting the bag since it fits in one. Took the took off and I love it. This would be great if you have limited space and have to stack, say cat and dog food separately. I love the wheel and the added scooper is a plus.