Saddle Pad Sizes?

Most of the time the pads are sized the same as the saddle. Look for one that is made to fit a 17" saddle. If they're not sized in inches, see if there's a chart that compares S,M,L to saddle measurements. I would guess that in most pads a 17" would be L. M is usally for 16-16.5, S is for ponies.