Soft recovery collar is machine washable and reflective at night. Includes adjustable collar for secure fit and added "stays" for strength. Small - pet's neck circumference 8-12 inches, Medium - pet's neck circumference 12-15 inches, Large - pet's neck circumference 15-18 inches, X-Large - pet's neck circumference 18-23 inches. To find the perfect fit: 1) Measure the smallest part of your pet’s neck starting from the back, 2) If your pet’s measurement is in between sizes, always use the larger size.