XS is for 6 to 8 inches
But my Pixie is 10 inches and she wears an XS, she is very Petite
She would be SWIMMING in a small! Its not meant to cover the butt. on a 10 in long body it falls nicely where a "hoddie" would on a person... on a shorter pup, it will fit longer providing more coverage and warmth! It's shorter on the belly so that on a 6 to 8 in frame it is clear of the potty zone!
And I'm almost sold out on them,
I only have a couple left!