XS measurement around dog neck 9"-13"
actual size of bandana 18" length
S/M measurement around dog neck 11"-18"
actual size of bandana 23" length
L/XL measurement around dog neck 19"-24"
actual size of bandana 31" length
Be sure to choose size depending on tightness/looseness you desire and keep in mind you will need 3-4 inches to tie bandana.
note: Cooper's neck size is 21", she wears L/XL. She likes the loose casual vibe.