TL; DR: size Small fits my narrow 31-lb BC mix with a 23.25” ribcage perfectly; she is consistently this size in RuffWear items. REVIEW: I went to the store to buy the Front Range harness I’d been eyeing, but ended up so much happier with the Flagline harness! I’m glad I had my pup with me to try both in, as I was sure the Flagline would be too long for her. As you can see in the pictures, it’s not too long at all. I love that it has a handle for emergency lifts; it has a bit more length along her spine/ribcage, so doesn’t choke up on her armpits/shoulders; it has a spot for her safety light; is almost infinitely adjustable size-wise; and it is really lightweight, which is perfect for my girl. I would trust the construction for any supervised dog including pullers, but this is not a harness to leave on an unsupervised chewer (tho tbh any chewer can make fast work of ANY harness, so …). My pup can be worried/skittish at times, and this harness feels very secure and also lightweight enough that she doesn’t seem to worry about feeling “trapped” in it. Bonus, I LOVE this color—granite grey with pretty light blue webbing that looks great and makes the straps and clips visible against her black coat. I’ve been training dogs for close to 30 years now, and have literally vested thousands of dollars in “dog tack” for my own use and my clients’. I am consistently impressed by RuffWear ‘s designs and build quality, and the Flagline harness is my favorite product to date! (Katie-Bug…