Widest part of Rib Cage
Inches
Centimetres
3XS
9-13
23-33
XXS
13-17
33-43
XS
17-22
43-56
Small
22-27
56-69
Medium
27-32
69-81
Large
32-36
81-91
XL
36-42
91-107
Note:
If your dog is in between sizes then choose the larger size.