Collar size:
S: neck 8.5-10.5 in (22-27 cm), width 0.5 in (1.3 cm).
M: neck 10.5-12.5 in (27-32 cm), width 0.5 in (1.3 cm).

Notice:
When measuring length, please set aside a little more, avoiding the pet feels uncomfortable because the collar is too tight.