Four Paws Products - Cool Things for Your Dog! Four Paws harnesses provide owners with a secure, comfortable, and controlled way to walk their pets Made of durable lightweight neoprene mesh Adjustable nylon strap offers the perfect fit Back hook harness allows extra control without the tugging X-Small - 3-4 lbs. 11-13" chest. 7-8" neck. Small - 5-7 lbs. 14-16" chest. 8-10" neck. Medium - 7-10 lbs. 16-19" chest. 10-13" neck. Large - 11-19 lbs. 19-23" chest. 13-15" neck. X-Large - 20-29 lbs. 20-29" chest. 15-17" neck. XX-Large - 29-40 lbs. 29-35" chest. 17-20" neck.