Size 18, length 18 inches, girth 23" - 28.5". The rcpets web site suggests a weight of dog 30 - 35 pounds. Typical breeds for this size according to the rcpets web site are the Wheaten Terrier, Scottie and Beagle. But since my 16 pound bichon Max fits size 16 and he is 16 pounds, I am thinking that perhaps a bichon over 20 pounds would fit it rather than the web site suggestion of 30 -35 pounds