The original SENSE-ation Dog Harness is a no-pull dog harness that works wonders for positive reinforcement dog training, or just taking gentler walks with your pooch. An instruction booklet comes with all SENSE-ation Harnesses. allowing you to take gentler, more enjoyable walks with your pooch. An instruction and training booklet comes with all SENSE-ation Harnesses. The SENSE-ation Dog Harness uses a custom polyester webbing for superior comfort. Features Duraflex plastic hardware and nickel plated O-rings on the chest and sides. The curved side-release buckle and strap keepers are a plus. The girth strap*, also called a "belly strap" comes in a coordinating color, making it easy to identify, and therefore easier to put on. *Please note: Extra Small Narrow and Mini size harnesses are all one color. The SENSE-ation Harness stops your dog from pulling, without choking, stress or otherwise harming your pet. You can use it right away - there is no acclimation period. Best of all, the SENSE-ation Harness is a favorite of positive reinforcement dog trainers and humane societies worldwide. Awarded "Gear of the Year" by The Whole Dog Journal, 2003. Using a flexible measuring tape, measure from just behind the front legs all the way around your dog. You are measuring the circumference of the body just behind the front legs, like performing a chest or belt measurement on a human.  Extra Large - 1 Inch Width 39 - 50 Inch girth*. Large (Wide) - 1 Inch Width 32 - 40 Inch girth*. Large (Narrow) - 3/4 Inch Width 31 - 40 Inch girth*Medium/Large (Wide) - 1 Inch Width 27 -32.5 Inch girth*Medium/Large (Narrow) - 3/4 Inch Width 26 - 32 Inch girth*Medium - 3/4 Inch Width 24 - 28 Inch girth*Small - 5/8 Inch Width 20 - 24.5 Inch girth*X-Small (Narrow) - 7/16 Inch Width 16.5 - 20.5 Inch girth*X-Small (Wide) - 5/8 Inch Width 16 - 20.5 Inch girth*Mini - 7/16 Inch Width 13 - 16.5 Inch girth** If the measurement falls within two harnesses, we suggest the larger size. Example: 20" girth = Small.