ADULT SIZE USERS. . . . . . . . Hello, it may be a mistake to determine a size for the product based on height, kg or age, and it will force you to deal with the return and cause you to waste time. When you look at the product pictures in order, there will be a size chart. It would be better to measure the knee cap circumference and order according to the result. Thank you, product size chart and Be sure to review and watch the product video. CHILD SIZE USERS. . . . . . Hello, please order according to the age group in the product size chart. What you need to pay attention to here is whether the child's height and weight are compatible with his or her peers. For example, the child is 10 years old, but he is big compared to his peers, he is like 12 years old, then order for a 12 year old, or the child is 12 years old, but he is skinny, he looks like he is 10 years old, then order for a 10 year old. It is impossible for us to make a clear estimate based on the height and kg written here. You have more information. If you are buying it as a gift, it would be clearer if you ask the other party.