Bighorn sheep horn measurement locations (D1D4) and horn length.
Boone and Crockett sheep scoring measurement location examples for D1D4 and horn length. Source: Boone and Crockett
Bighorn sheep horn length measurement chart example from 32" to 43 7/8". Source: Boone and Crockett
Bob Oconnor's Nelsoni Desert bighorn sheep live photo.
Bob O'Connor's desert bighorn sheep from Arizona's Unit 15D.
 Longest hornlength 

Inches  39 1/8" 
Quartermeasurementlocation 

 Shortest hornlength 
Inches  38 4/8" 
Quartermeasurementlocation 

 D1  left 
Inches  15" 
Quartermeasurementlocation  0" 
 D2 left 
Inches  14 2/8" 
Quartermeasurementlocation  9 25/32" 
 D3  left 
Inches  12" 
Quartermeasurementlocation  19 9/16" 
 D4  left 
Inches  8 4/8" 
Quartermeasurementlocation  29 11/32" 
 D1  right 
Inches  15" 
Quartermeasurementlocation  0" 
 D2  right 
Inches  14 1/8" 
Quartermeasurementlocation  9 25/32" 
 D3  right 
Inches  10 5/8" 
Quartermeasurementlocation  19 9/16" 
 D4  right 
Inches  8 4/8" 
Quartermeasurementlocation  29 11/32" 
 Left masstotal 
Inches  88 7/8" 
Quartermeasurementlocation 

 Right masstotal 
Inches  86 5/8" 
Quartermeasurementlocation 

 Grossscore 
Inches  175 4/8" 
Quartermeasurementlocation 

 Net score 
Inches  174 
Quartermeasurementlocation 

 Inches  Quartermeasurementlocation 

Longest hornlength  39 1/8" 

Shortest hornlength  38 4/8" 

D1  left  15"  0" 
D2 left  14 2/8"  9 25/32" 
D3  left  12"  19 9/16" 
D4  left  8 4/8"  29 11/32" 
D1  right  15"  0" 
D2  right  14 1/8"  9 25/32" 
D3  right  10 5/8"  19 9/16" 
D4  right  8 4/8"  29 11/32" 
Left masstotal  88 7/8" 

Right masstotal  86 5/8" 

Grossscore  175 4/8" 

Net score  174 

This article is going to go indepth on how to score bighorn sheep. Keep in mind this article applies to all bighorn sheep including Rocky Mountain, California and desert bighorn as well as the thin horn sheep including Stone and Dall. The method of scoring bighorns will be the same for every bighorn species. In a prior article, I covered how to age a ram now let’s go over what makes up a bighorn sheep's total score.
To keep it simple, there are four mass measurements for each horn; which are the circumferences around the horn (8 total) and one length for each horn (2 total).
The first step is to measure the lengths of each horn. Next, determine where each mass measurement needs to be taken based on the length of the longest horn. See the horn length chart example below for measurement locations.
Bighorn sheep horn length measurement chart example from 32" to 43 7/8". Source: Boone and Crockett
Take the length of the longest horn and divide it by four. Let's use a 36” horn as our longest horn so 36 divided by four equals 9”. Based on this example, there will be a measurement taken at 0 (base) or D1, at 9” or D2, at 18” or D3, and at 27” or D4. The first mass measurement is always taken at the base of the horn where it meets the head, which is called the "D1" measurement on the Boone and Crockett (B&C) score sheet. Then, you continue 9” down the length of the horn to the second measurement and so on for the third and fourth.
One thing that confused me when I was first learning about how to score sheep is figuring out what/where these quarters actually were. In essence, what they are talking about is D2, D3 and D4, but with sheep lingo, those quarters are referred to as base, first quarter, second quarter and third quarter.
In order to calculate one side or one horn total, first add the mass of each side and horn length of each side. Then, add both horn totals together for the gross, or total, score. Once that is done, compare each mass measurement to the other horn and deduct the difference to get the final net score. You do not deduct horn length, only each circumference measurement.
For this example our longest horn is 39 1/8 ”and the shorter horn is 38 4/8”. Start at the base of the horn, then measure 9 25/32", then 19 9/16", and finally 29 11/32".
Side note and more of a field judging tip: the mass measurements (D1, 2 ,3, 4) of each horn makes up about 60% of the total score of your ram so finding a ram with good mass is essential to a high scoring trophy.
Spread is measured for the B&C scoring system, but does not fall into the equation for scoring.
The length of horn is measured from the lowest point in front on the outer curve to a point in line with the tip. Do not press tape into depressions. The low point of the outer curve of the horn is considered to be the low point of the frontal portion of the horn and is situated above and slightly medial to the eye socket (not the outside edge). Use a straight edge, perpendicular to the horn axis, to end the measurement on broomed horns.
The circumference of the base is measured at a right angle to the axis of the horn. Do not follow the irregular edge of the horn; the line of measurement must be entirely on horn material.
Divide the measurement of the longer horn by four. Starting at the base, mark both horns at these quarters (even though the other horn is shorter) and measure the circumferences at these marks, with measurements taken at right angles to the horn axis.
Try to resist the urge to score the ram when at the harvest site and when the hair is still on the head as it is hard to get an accurate reading and, often times, leads to a score bigger than the actual score, which can make for awkwardness.
Desert bighorn: 168”
Rocky Mountain bighorn: 180”
Dall sheep: 170”
Stone sheep: 170”