Do you mean human butt size? Mines a 16.5. If you mean like QH or semi Qh bars
Mine is a gaited horse tree. There is a man, Don West who years ago developed a gaited horse tree for short backed Paso Fino type horses. That's the tree I have.
HAHA Vida! I have more saddles than horses.. sigh.. tack hog is what I am... But, my own personal I love it saddle is probably a medium(western) so... semi QH bars.. It seems to fit about any of them fairly well. Fits Abe great.. I also have what seems to be a wide tree synthetic (abetta, I think). I don't use it much but it's comfy for me. The aussies are paneled so? Dunno, but they fit my semi horses anyway.