To find the perfect size for your dog,please measure your dog's neck circumference in the position shown on the diagram. These collars have bands of 3M Scotchlite reflective material that provides good visibility to the dog and its owner. The metal ring is durable with large loading capacity and tensile strength to suit even large dogs. The buckle is made of lightweight Duraflex plastic for easy,one handed release,preventing cases of accidental unbuckling. The soft breathable mesh lining with padding is ultra-comfortable. Sizes are fully adjustable for best fit. Scroll down below and look at the product to find the perfect fit for your dog. Size --Collar Width---------Neck Length 2X-Small 1.5cm / 0.6in 28-30cm / 11.0-11.8in X-Small 1.5cm / 0.6in 30-35cm / 11.8-13.8in Small 2.0cm / 0.8in 35-40cm / 13.8-15.7in Medium 2.0cm / 0.8in 40-45cm / 15.7-17.7in Large 2.0cm / 0.8in 45-50cm / 17.7-19.7in X-Large 2.5cm / 1.0in 50-55cm / 19.7-21.7in 2X-Large 2.5cm / 1.0in 55-60cm / 21.7-23.6in 3X-Large 2.5cm / 1.0in 60-65cm / 23.6-25.6in