While I might not be a very experienced hunter, I do have some tips that help me. Using reference points to compare antlers to will allow you to have a pretty close idea. A muley's ears are roughly 8 inches long and about 20 inches from tip to tip. If yo have a deer with a rack that looks to be about 3 inches outside of his ears and with tines that are close to ear length, assuming its a traditional you can figure about 90 inches without mainbeam or mass measurements. For a mass reference, use the deers eye. It will have a surcumference of approximately 4.5 inches. If the beams look to be at least as thick as the eye throughout, figure another 16-18 inches per side. That brings the estimate to 126. Using the ear reference and assumption that mainbeam length is shorter than spread, you might figure a length of 23 inches or so. Add it all up and you get an estimated 172 inch deer. I hope I articulated that clearly and added correctly, haha.
I was using a typical 4 point as my example and the measurements I came up with were as follows:
G1: not counted to balance over inflation.
G2: 16 inch
G3: 8 inch
G4: 8 inch
Four mass measurments of 4.5 inch
Spread 26 inch.