The best way to determine the correct size collar for a horse is to ask your collar-maker to measure it accurately with their collar gauge (the length, distance between the draught-turns & distance between the neck-turns, all in inches).

If that is not possible, there are a couple of other ways:

1. Borrow a range of old collars to find one that is close to fitting. Measure the inside of the rim of this collar with an inch rule, supplying the collar-maker with the three measurements shown in the image above.

An example of a well-fitting collar is displayed here:

OR

2. Use a couple of large carpenters’ squares to make your own makeshift collar gauge. To get the approx. length, place the two squares together [like the letter ‘C’] several inches in front of the horse’s withers, with the bottom of the C several inches away from the horse’s chest/shoulders, & the top of the C resting several inches in front of the withers [you are guessing where the body of the collar will eventually lie against the horse’s “collar bed” (from in front of the withers to above & in front of the points of the shoulder)];

Slide the two long sides of the squares together up & down until you have the correct length. Note that you must also allow an extra two fingers distance – on their edge – between the horse’s windpipe & the inside of the throat of the collar; ie. one needs to add this distance to one’s measurement with the squares. Someone would need to help you with this [for example, they would need to measure – with a separate rule – the distance between the inside top & bottom of your C]. You need to repeat this procedure to determine the draught-turn & neck-turn measurements, adding the distance of the flat of your hand to these two measurements.