How do you check if a western saddle fits the rider correctly?

Saddle fit for the rider is discussed far less frequently than saddle fit for the horse, but a saddle that does not fit the rider correctly makes it impossible to sit correctly, apply aids effectively, or maintain the balanced position that a well-trained horse needs in order to perform at his best. A rider struggling against an ill-fitting saddle compensates with tension, gripping, and postural distortion that translates directly to the horse as unclear or contradictory communication. Seat size is the starting point for rider fit. In a western saddle, the correct seat size allows the rider to sit in the center of the seat with approximately four fingers' width of space between the back of the rider's seat and the front of the cantle. Too large a seat leaves the rider floating without support, unable to maintain position through transitions or quick maneuvers. Too small a seat jams the rider against the cantle, restricts hip mobility, and pushes the rider into a chair seat that makes following the horse's movement nearly impossible. The seat depth and shape should suit the rider's anatomy and the discipline. A deep, secure seat suits riders who want maximum stability for roping or ranch work. A flatter, more open seat gives the flexibility needed for cutting or reined cow horse work where the rider must move with the horse dynamically. A seat that forces the rider into an unnatural position — tilting forward or backward, tipping to one side, or pinching the thighs — is not a fit problem that stirrup adjustment or pad changes will solve. Stirrup position relative to the seat also affects rider fit significantly. If the fenders and stirrups hang in a natural position that places the stirrup directly under the rider's center of gravity without twisting the knee or ankle, the saddle is built on a tree that suits the rider's proportions. Fenders that must be twisted significantly to align with the rider's foot are a chronic source of knee pain that many riders incorrectly attribute to their own flexibility limitations rather than equipment mismatch.