XS: chest 35-46cm, neck 28cm, 2.0cm straps, suggested weight 4-7kg
S: chest 43-55cm, neck 36cm, 2.0cm straps, suggested weight 7-12kg
M: chest 52-67cm, neck 41cm, 2.5cm straps, suggested weight 12-20kg
L: chest 64-84cm, neck 45cm, 2.5cm straps, suggested weight 20-35kg
XL: chest 75-100cm, neck 53cm, 2.5cm straps, suggested weight 35-55kg
Measure the base of the neck and the widest part of the chest behind the front legs. The neck opening is fixed and the chest strap adjusts. Allow for a 1-2cm measurement variation.