I thought I could fit four 500ml PET bottles in it, so I measured the inside of the fridge before buying two of them, but the height of the shelves wasn't enough to fit two bottles on top of each other in a fridge for one person... I was too careless with the measurements and checking. It's not a size that can fit 750ml PET bottles either, so I thought it would be nice if they made a slightly shorter type that could fit 500ml PET bottles. For now, I'm using one box and forcing the other two bottles on top of the two bottles that fit in the box. Thanks to the extra height, I've managed to fit them in. I used the other box for something else in the fridge. It's so easy to take things out, I think I'll start using boxes like this for storage.