Size XXXS: neck 20-25cm, width 1.2cm
Size XXS: neck 24-32cm, width 1.5cm
Size XS: neck 29-37cm, width 2.0cm
Size S: neck 38-46cm, width 2.5cm
Size M: neck 49-57cm, width 3.0cm
Size L: neck 56-66cm, width 3.5cm
Measure the widest part of the neck, around the middle where the collar sits, and choose the size whose range your measurement sits inside, ideally near the middle. Measurements are taken by hand, and a difference of 1 to 2cm is normal. There is a gap between S (up to 46cm) and M (from 49cm): a dog measuring 47-48cm should take M. Once buckled, two fingers should slide flat between the collar and the neck. New leather is firm at first and softens over the first few weeks.