The Shabby Dog Sizing Guide:

 
 

Collar:

 
Size Wide Long
XSmall 1/2" 8"-11"
Small 1/2" 11"-14"
Medium 3/4" 14"-17"
Large 3/4" 17"-20"
XLarge 1" 20"-23"
XXLarge 1" 23"- 26"
 

Harness:

 
Size Neck Girth
XSmall 7"-8" 11"-12"
Small 8"-9" 13"-14"
Medium 9"-11 15"-16"
Large 11"-12" 17"-19"
XLarge 13"-14" 20"-22"

If you are not sure, please call us at 877-800-8181 to speak to a customer service representative.