Harness Size Guide:
XXS 
Neck Girth: 22cm to 31cm
Chest Girth: 28cm to 38cm
XS 
Neck Girth: 29cm to 36cm
Chest Girth: 36cm to 48cm
S 
Neck Girth: 35cm to 44cm
Chest Girth: 41cm to 54cm
M 
Neck Girth: 39cm to 51cm
Chest Girth: 46cm to 61cm
L
Neck Girth: 42cm to 56cm
Chest Girth: 57cm to 83cm