How to choose your size Measure the height or shin length from below the kneecap to the top of the foot. If information is not available, use age to determine size. Shin Length Shin Size 7 - 8 Inches = S is recommended Shin Size 8 - 10 Inches = M is recommended Shin Size 10 - 12 Inches = L is recommended Height: Size S - for child up to 3'11" tall Size M - for child up to 4'7" tall Size L - for child or adult up to 5'4" tall Age: Size S - for child 3 - 6 Years Size M - for child 6 - 10 Years Size L - for child 10 - 14 Years