Helmet sizing for youth

Im looking for the right size helmet for my son,  He is only 8 years old., please help?

i think you need to bring your son to a shop and try on the different helmets. same-size helmets, even made by the same company, fit differently. so, without actually trying it on, you'll never know if it actually fits right. everybody's head shape is different, so one helmet that fits one 8yr old, may not fit another 8yr old, even with the same head size. after knowing which helmet fits your son, then you can go find the cheapest price on the internet and buy that specific model/size.