The Small Michelle will fit most 24oz cups and bottles! The Medium will fit most 32-40oz cups. The Large will fit most 40oz cups. While the 24oz Starbucks Cold Cup will fit in the small, the straw will stick out the top so we recommend pairing it with the Medium for a more flush fit. STANLEY USERS: this will fit in the medium size but will stick out of the top of the bag. Due to this we recommend using the Large size for all Stanley 40oz adventure quenchers, or 40oz Owala tumblers with the handle.