I purchased this online for my son who wears a size 4-5. I bought an small which is an 6-7. My son is broad in the shoulder which this fit him perfect but I found the length to be a bit long. The sleeves are bit longer than I expected but for sun protection I find this is a plus. It doesn't state on the website but when arrives the shirt is SPF protected. The shirt is thinner than I thought but that may be a bonus when it get too hot.