“Short stature is defined as a height more than two standard deviations below the mean for age (less than the 3rd percentile).
Tall stature is defined as a height more than two standard deviations above the mean for age (greater than the 97th percentile).”
Reference
Am Fam Physician. 2015 Jul 1;92(1):43-50. Evaluation of Short and Tall Stature in Children. https://www.aafp.org/afp/2015/0701/p43.html.