how to tell if a saddle is too narrow?

 
How to tell if a saddle is too narrow?
The pommel will be too high above the withers, therefore offsetting the rest of the saddle on the horse's back.

Examples of saddles that are too narrow:

http://therefinedequine.com/yahoo_site_a…

http://www.equestrianimports.com/shop/im…
The pommel will be more than a few fingers above your horses withers. You can also feel if it is pinching your horse by sliding three fingers underneath the front. If you cannot easily do this then it is too narrow. It is easier to tell without a pad or girth. Do not try to over pad a saddle that is too narrow as this will cause more pinching. Saddle fitting is an art, and if you are still unsure you can contact a professional saddle fitter.
As the people above me said, check the pommel(sp?)
pets question and answers,www.5d2d.com

A way to look for this another way is just lunge your horse briefly...if your horse appears to have trouble striding out and completely stretching while at a trot ( or even a walk! ) then it is too narrow and is causing problems. Alot of times, a horse will misbehave out of discomfort due to an ill-fitting saddle.
But do check the pommel, that way you are not causing unnecessary discomfort, though a round or two lunging shouldnt be too terrible.
I hope I could help!