"Small bladders" don't really exist.

When someone says they pee a lot because they have a small bladder, this isn't really true. Bladders don't vary much in size, but it could be how your bladder is acting instead of its actual size. Feeling like you have a small bladder may have to do with how much your bladder can hold and how long you wait before peeing. Some people will sense bladder fullness at an earlier time than others, and that’s why they think they have a small bladder. You might get that message to pee very soon after it’s empty and starting to fill.