There are 3 sizes for choosing :
Small: neck girth 11-13.0",fit neck 9.0-11.0",suitable for 10-16 lbs dogs,
Medium:neck girth 12.5-15",fit neck 10-13.0",suitable for 16-21lbs dogs
Large: neck girth 14.2-17.3",fit neck 12-15.0",suitable for 19-28 lbs dogs（even if this size was named as size large ,in fact ,it isnot suitable for large dogs ,such as lab,pitbull,boxer etc.)
Please measure the dog's neck girth refer to the size chart.
Better give 1-2cm extra room for the neck