My dog is a 90-100lb mix that’s about the size of a golden retriever or German shepherd, and the large works perfectly for him. It took a few minutes to figure out the best way to adjust the buckle straps and to re-wrap the straps up into the velcro part, but once I figured that out it works great. And I actually appreciate that part of the design too, it keeps excess strap length out of the way and organized!! I slip the life jacket right over his head and buckle it up and he’s ready to go!