The original SENSE-ation Harness is a no-pull dog harness that works wonders for positive reinforcement dog training, or just taking gentler walks with your pooch. The SENSE-ation Harness comes in seven sizes and two colors - dark purple (with a black belly strap) or all black. An instruction booklet comes with all SENSE-ation Harnesses. The SENSE-ation is similar to the SENSE-ible Harness in design, however the SENSE-ation uses a custom Softouch polyester webbing for added comfort. The SENSE-ation Harness also features Duraflex plastic hardware, instead of metal. The O-rings on the chest and sides are nickel plated steel for extra durability. 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. 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 j behind the front legs, like performing a chest or belt measurement on a human. X-Large 1 Inch Width 39 - 50 Inch girth*. Large - 1 Inch Width 32 - 40 Inch girth*. Large - 3/4 Inch Width 31 - 40 Inch girth*. Medium/Large - 1 Inch Width 27 -32.5 Inch girth*. Med /Large - 3/4 Inch Width 26 - 32 Inch girth*. Medium - 1/2 Inch Width 24 - 28 Inch girth*. Small - 5/8 Inch Width 20 - 24.5 Inch girth*. X-Small - 7/16 Inch Width 16.5 - 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.