TO GET THE BEST POSSIBLE FIT BECAUSE EACH PRODUCT HAS DIFFERENT STRETCH AND ETC...EACH PRODUCT WILL HAVE ITS OWN PERSONAL SIZE CHART FOR SIZING. ALL YOU HAVE TO DO IS CLICK THE MORE BUTTON AFTER THE DESCRIPTION AND IT WILL TELL YOU THE SIZES FOR THAT PARTICULAR ITEM. THEN YOU CAN MEASURE YOUR PET TO YOUR BEST ABILITY AND MAKE A SIZE CHOICE FROM THERE!!!