I ordered a Large and it fits my 78lb Rottie mix with strap length to spare. Length wise she it doesn't cover her entire back, but it does cover sides. It is waterproof so what is covered stays dry (it's not sold as a raincoat)
I live in a rural subdivision with no street lights, and this vest lights up in car headlights like a fishing trawler at midnight, the dog can be seen from at least 1/4 mile away, possibly further.
So between the dogs vest and my safety vest we make quite a spectacle on the streets at night.

This reflective dog vest is VERY reflective. Our beagle loves to hike with us in the woods and she wears this vest so we can see her from far away. She is slim and weighs about 29 lbs and the small fits her perfectly. We've washed it twice and it's starting to fray slightly but she's been wearing it all winter, several times a week so I feel it's held up pretty good. The vest is very reasonably priced so I wouldn't mind buying a new one every year or two if needed. Love it.

Great product, reasonable price. Very happy with it. FWIW, when it first arrived, dog was thrilled. As others mentioned, she came running to put her head in and gladly wore it. After a couple of days this changed- turned her head away and fussed. We discovered lots of her long Irish Setter hair in the velcro and it was hurting her when velcro was undone. Also, our Irish is large, and I am not, I had some problems reaching around her, where I can't see, with my face on her neck to fasten the vest. (Picture funniest home videos) Anyway, I took the strap off, arranged it so that none of the hook portion of the velcro touched her and restitched it. It now fastens on her back instead of her tummy.Better for both of us. We are back to happy dog, wearing this highly visible, comfie, lightweight vest. Days are short, hunting seasons long here, we are both safer when she is easily seen. Only reason 4/5 stars is that inconvenient strap fastening. Ddonot understand other comments of flimsy and poor stitching. Isew a lot some commercial, and this thing had stress stitching at several points and was hard to take apart to change the strap. It IS sturdy. Our rambunctuous Irish runs through brush/woods/water with gusto, too.

This is a great reflective vest! Size Small fits our 22-pound muscle-y mini schnauzer just right. (Not that he likes wearing it, though.) The velcro straps are long and that makes them highly adjustable. Construction of the garment is very good. This is a great addition to his wardrobe and will improve his chances of NOT getting shot during hunting season and of NOT getting hit by a car at night! Double goodness.

exactly what I was looking for. Fits my GSD well, she's a big-boned German bloodline and weighs 70 lbs and it fits her across the chest and neck with room to spare and ends about where her back hips begin (somewhere around 6 or so inches before the tail base) so it covers most of her back. I am really using it for walking at night and also during fireworks as she grows anxious during fireworks (Fourth of July and New Years in this area are noisy nights) A lightweight jacket makes her feel more secure and eases her anxiety. Weird but it really works, I borrowed one from my doggy sitter on Fourth of July after he recommended it and it worked miracles! I decided to buy her a jacket of her own and had a tough time finding one that was lightweight enough for Florida heat and fit her girly physique ;] This works great and I am looking forward to trying it out on New years when my neighbors go crazy with the fireworks again. The fabric is nice, kind of a light rain jacket feel to it and it does reflect well when light hits it at night so I would recommend it for that purpose as well.