Bought the large size for my cat who weighs apprx 6kilo. I am very impressed with the quality of the bag, it is very well made, sturdy and does not crumple even when carrying on the shoulder. It is possibly a bit too big but the dimensions of the medium one seemed too small. So much easier to carry than a basket. Because of the quality fabric used, it is a tad heavy, but using the shoulder strap alleviates this.