Adult to fit chest (inches): XS (34"), S (36"), M (40"), L (44"), XL (48"), 2XL (52"), 3XL (56")
See size guide in photos. The T-shirt is a unisex fit and the ladies sizes are only an approximate reference.
If you would like a more fitted look we would recommend going down a size.
Model is a size 8 and is wearing an extra small