Bandanas are designed to slide over your existing pets collar no need to tie around their neck just slide through and clip as normal! Size small in picture on 1 year old Corgi. 
S
7.5-8 in across collar 
5-5.5 inches down back 
M
10-10.5 across collar 
7.5 inches down back  
L
13 across collar 
9 down back