The gullet size on Western saddles can be confusing, basically measurements go 2" larger than normal english saddles. (So a 16" western is up to an 18" English equivalent). Bars = gullet size. Full QH bars is a wide gullet.
Generally the size refers to the seat. Occasionally there are shorter skirts on them but they're all around the same length.
Main thing with fitting a western saddle is the gullet size & whether your horse would suit a full QH bar (wide shoulders) or a semi-QH bar (anything less than wide, really). The fit is very different to English saddles.
To make it more confusing - there are alot of western saddle brands out there and they are all slightly different in fit. We are currently offering 10% off all our western saddle range with discount code BLOG10.