The ultimate goal of saddle fit is to have the saddle that fits both the horse and rider, more importantly the horse.
There is no industry standard when it comes to tree sizes so different saddle brands will not fit the same and may vary among disciplines. So it's important to have some basic knowledge about saddle fitting.
There are many factors that come into play when checking the fit of your saddle on your horse.
The 2 main factors are gullet width and bar angle.
Gullet Width: is often misunderstood. Gullet width is the measurement under the fork between the side conchos. Keep in mind this won't be entirely accurate as saddle makers determine gullet width on a bare tree.
A narrow gullet will sit higher on a horses wither vs a wide gullet will sit lower.
Bar Angle: is often ignored. Bar angle is basically self explanatory. It's the angle of the bars on a saddle. They need to match the angle of your horses back as closely as possible.
A narrow angle will make contact at the bottom of the bars but not the top and a wide angle will make contact at the top of the bars but not the bottom.
The gullet width should be about the same width of the withers, 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!