I have two 70 lb dogs, & switched the size up from 3x to 4x at the last minute and they're a little big, but that's my fault. 1 of them was a mistakenly a 3x and it fit perfect. Lesson learned, go by the sizing chart not your gut. That being said, we live in the hot desert and these light colored , light weight shirts are perfect for my black dogs. Great quality, would absolutely buy again.