The gullet of a saddle is the part that spans the withers and spine of the horse. By some definitions, it extends the entire length of the saddle, but the measurable part is at the front. Australian saddles are built in three basic gullet sizes; narrow, medium and wide. When saddle retailers speaks of gullet size, they are actually referring to the distance between the bars of the tree beneath the pommel. The pommel is the swell at the front of the saddle where a horn might be attached.
Place the saddle on a stand or sawhorse. Looking from the front, you should be able to visually determine if it is narrow, medium or wide.
Use your ruler to measure across the front. Start about four to six inches from the top, or point, of the saddle pommel. Gullet widths range from about six inches, which is average, all the way up to 10 inches--usually designed for drafts and mules.
Place the saddle on your horse. There should be two to four finger-widths between the highest point inside the pommel and your horse's withers. If there is more, your horse needs a wider gullet; if less, it needs a narrower gullet.
The best way to determine the gullet size is by trying the saddle on your horse. An Australian gullet is measured in the same manner as an English saddle gullet.
A poorly fitting saddle can cause injury to you and your horse. Please consult a professional for a final word.