Shein Kids has one of two options for product sizing. They either list the product size by age (2Y, 3Y, 4Y, etec) or they offer centimeter sizing that looks something like 80, 90, 100, etc. Here is a good guide for converting your child's regular US size into centimeters.  US size 2 = 80 US size 3 = 90 US size 4 = 100 US size 5 = 110 US size 6-7 = 120 US size 8 = 130 Shein sizing used to run small but do not size up anymore. Things run true to size. Shein also has sizing info on their site and you can see actual measurements for each size if you want to be 100% sure.