Some people will use the following methods to predict how tall their young horses will grow to be. While it's not always accurate, it does give a good estimate, and it's fun to do!
Method #1: Elbow/Fetlock
The first one is of a mature horse and the second is of a young horse
Because the distance from a horse's point of elbow to its fetlock is approximately the same as the point of elbow to the withers, you can use this method to predict height in young horses. Take a leadrope and stretch it from the point of the elbow down to the fetlock. Now that you've got the distance, keep your hand on where the fetlock measurement is (leave the other end on the point of elbow) and bring the leadrope up to the withers. That's about where your horse should mature to.
Take a soft cloth measuring tape (like the kind used for sewing) and measure from the middle of the knee to the coronet band. However many inches, is how tall in hands the horse will grow. Each 1/4 of an inch is .1 hand.
So if you get 14 3/4 inches, the horse will be about 14.3
15 1/2 inches, the horse will grow about 15.2
16 1/4 inches, the horse will be about 16.1
For this method you will need to know the height of your horse at the age of 2 then complete the formula below it is estimated that your horse will reach 90% of his height at this age. I am using a height of 14 hands at 2 years of age below plug in the height of your horse at two in the hands area on the left
The 14 hand 2 year old is estimated to reach 15.2 hands at adulthood (as .5 is equal to half of the 4 inches per hand so it is .2 hands)