The Calming Cap is a wonderful tool for easing a dog"s anxiety in high-stress situations. The calming cap reduces visual stimuli and helps dogs to remain comfortable, overcome fearfulness and increase their confidence. The single-panel sheet fabric window does not blind dogs, but simply filters their view. Try it for yourself - you"ll see that while your vision is somewhat limited, you"re still able to comfortably and assuredly make out shapes. Quality Features: Single-panel sheer fabric allows ample vision for dogs to confidently maneuver around while reducing any provoking stimuli. Soft fabric and elastic fit provide maximum comfort. Two adjustable straps allow for easy on/off use. Use with a Thundershirt when more calming is needed. X-Small Snout Circumference - 3" - 6". Distance from "between the eyes to collar - 2.5" - 5" Small Snout Circumference - 5" - 8". Distance from "between the eyes to collar - 5" - 9" Medium =Snout Circumference - 7" - 10". Distance from "between the eyes to collar - 7" - 12" Large. Snout Circumference - 9" - 12". Distance from "between the eyes to collar - 9" - 16" If unsure between sizes, go with LARGER size.