My average size baby is 8 months old, so I got the 6-12 month old size.
However, it was nearly 3 inches too short-!!!

Otherwise, the item is excellent - I love the organic the material which is smooth and soft against the skin, and shows high quality stitching. The graphic is not great, it is slightly out of scale)

My recommendation is that you can consider purchasing if your baby is about 2 months younger than the size group represented.