Purchased size large as my bearded collie cross old English sheep dog named Stella is 30 kg but 90 cm in the chest. This chest measurement is the upper limit for the large harness. I found this tended to be too tight on her, so after a week of trying this size of harness, I purchased the xl size. This has worked out much better for both of us. Stella, a natural herder of cats, deer and the occasional black bear, is much easier to control during our trail walks with this harness. I would recommend this harness for any dog that tends to pull.