The two most critical measurements on a Western saddle is the gullet width and the bars.

Gullet – to accommodate the horse’s spine

The Bars of the Western saddle tree

The above image demonstrates how the bars flare out to accommodate with width of the horse’s back.

Western saddles are made in basically 8 gullet sizes (see below),  which cannot be mechanically widened from one size to another, as can many English saddles.  It is therefore ultra-important that your used Western Saddle fits your horse as well as yourself, if you are the main rider.

So, the really critical measurement is up front where the bars join the fork in the area called the gullet. The gullet is the space which makes room for the horse’s withers.

Understandably, these two parts – the horse’s spine and the withers are the two areas where the saddle must NOT touch, especially when the rider’s weight is in the saddle.  Any pressure here will cause the horse GREAT discomfort and often lameness and at the very least a lack of performance.

You have to take into consideration both the WIDTH and the HEIGHT of the gullet in order not to cause any contact or pressure on the wither.

The bars – which run along the horse’s back, are separated by a channel (the gullet).  The height and width of the gullet are measured in inches.

Bar Angle and Gullet Widths.

Quarter Horse Bars –designed to fit narrower western horses which were common place up through the 1960’s. These bars have a narrow angle. Gullet width of 5 3/4″- 6″. 

Semi-Quarter Horse Bars-horses got bigger and wider from the 1970’s on, requiring a wider angle in the bars. Semi-quarter horse bars fit most of today’s western horses. Gullet width of 6″-6 1/2″.

Full Quarter Horse Bars- have even wider angles to accommodate wider-bodied horses and horses with flatter or “Mutton” withers. Gullet width of 6 3/4″- 7″.

The gullet width should be about the same width of the wither’s, approximately 2″ below the top of the withers. Just remember, the main thing you need to know is, is your horse narrow, wide or in-between!

If you ‘Google’ Western saddle width fittings you will come across a variance and the following list is regarded as a general guide to gullet sizes:

Regular Quarter Horse Bars (RQHB) – 5 3/4ins to 6 1/4ins

Semi Quarter Horse Bars (SQHB) – 6 1/4ins

Quarter Horse Bars (QHB) – 6 1/2ins – 6 3/4ins

Arab or Arabian Saddles – 6 1/2ins – 6 3/4ins

(but the difference between that and the QHB is that the bars are wider for the Arab horse conformation)

Full Quarter Horse Bars (FQHB) – 7ins

Haflinger – 7 1/2ins

Draft Horse – 8ins

For further information Wikipedia has a great description and explanation of how Western saddles are measured.