Medium: measures 18" between the rolls and 23" including the rolls.

Large: measures 19 1/4" between the rolls and 24" including the rolls.

As a general rule of thumb, most saddles up to 17.5" fit on a medium, however due to saddle and brand variety, please measure your saddle panels to ensure you select the appropriate size for proper fit and comfort for your horse. Your saddle panels must not hang over the ThinLine panels on the pad.