XS:20cm Outer Diameter: Fit for Pets Within 1KG/2lb

S:40cm (15.75inch) Outer Diameter: Fit for Pets Within 2.5KG/5.5lb

S:40cm (15.75inch) Outer Diameter: Fit for Pets Within 2.5KG/5.5lb

M: 50cm (19.69 inch) Outer Diameter: Fit for Pets Within 5KG/11lb

L: 60cm (23.62inch) Outer Diameter: Fit for Pets Within 9KG/20lb

XL:70cm (27.56inch) Outer Diameter: Fit for Pets Within 17.5KG/38lb

XXL: 80cm (32.5 inch) Outer Diameter: Fit for Pets Within 25KG/55lb

XXXL: 100cm (39.37inch) Outer Diameter: Fit for Pets Within 27KG/60lb

110CM（43.3inch）Outer Diameter: Fit for Pets More than 25kg or many pets.