Swim Zip Never Worn it does not have a size in it but I believe I boight the 6 to 12 month size. From SwimZip Site: Made of the highest-rated, most comfortable UPF 50+ sun protective fabric Blocks 98% of the sun’s harmful UVA & UVB rays for maximum sun protection 4-way stretch for extra freedom of movement Quick-drying and chlorine-resistant fabric Flat seams help to reduce rubbing Fabric: Nylon/Spandex