As a Taxidermist I look at hundreds of Whitetail Bucks every year. I know that I have seen many different ways people judge the size of racks on live deer. I think for the most part they all are pretty close. I'm going to give you some measurements that I have noticed being right on in just about every deer. We have used it in the last couple years and have only been off by about 5-6 inches. We do study the deer while bowhunting so we get a little more time to look at them.
Measurements to Remember:
1. Deer EARS are almost always 8 inches tall (this will give you a good TINE length).
2. Deer EARS are almost always 18 inches apart from tip to tip (this will give a good inside and outside spread).
3. Deer EYES are about 2 inches tall from the front part of the eye to the back (this is a great way to see how heavy he is at the base). If his rack is the size of his EYE he will be about 7-8 inches around at base.
4. 90% of all Mature bucks will have a measurement of 7- 7 1/2 inches from tip on NOSE to front part of EYE (great way to see how long main beams are).
I know that is a lot to look at but just using a couple of the measurement points can help.
Tip Nose to front of eye 7 1/4
25 inch main beams