A 10/12 in youth shirts typically corresponds to a Youth Medium (M) or Youth Large (L) in many clothing brands. Youth Medium (M): for children around ages 8-10, height between 48-58 inches, and weight around 50-70 lbs. Youth Large (L): for children around ages 10-12, height between 58-63 inches, and weight around 70-85 lbs. Check our youth size charts here.