Less than 20mm watch case sizes are considered very small. What watch size you want depends on a few different things. It could be because of the size of your wrist or it could just be your own preference as well. Maybe you want something unique and something that will not take up a lot of room on your wrist. Whatever your reason, we've got selections for you! On top of deciding the right watch size for yourself, you'll want to consider some other things like the case diameter and case thickness as well.