There really isnt a "formula" to measure a donkeys height, like there is for a horse, since donkeys can be born up to 3/4 of there mature height. All the "old timers" I have talked to in the donkey world and asked the same questin..all seem to agree , just take the birth height and add on anywhere from 9 to 12"s and that is there mature height. I know it dont give you more of a exact mature height, but I guess with our lovable longears..nothing is ever like "according to the books" with them. How tall was Molly when she was born?