How can you calculate child's height using parents and grandparents?

Simple measures: Expected height from parent stature is equal to the average parent height (m+d/2) + 2.5 inches for males, -2.5 in for girls.Grandparent height is not used but may point to variations in accuracy of the method. This is only a basic predicted height. Some very tall or very short people come from normal sized parents, & a life's medical & nutritional issues can slow the growth of anyone.