How to depict size of items so customers finally get it?

I sell planner stickers that are 1/3 inch to 1/2 inch. They are meant to be tiny to allow writing space in the planner. I have photos showing it next to a penny, stuck on the tip of a pen, and a dimension line going across saying 1/2″. It is in the title and description. But I still get public complaints and returns saying smaller than described. Can anyone share a tactic that actually works that actually registers with customers about sizing?