MEDIUM - 1” Wide x 13-17” Long
LARGE - 1” Wide x 17-21” Long
X-LARGE - 1” Wide x 22-27” Long
To get the most accurate size collar, measure the center of the neck with a cloth tape measure, a few inches down from the head. If you don't have a tape measure, you can also use a piece of string and measure it with a ruler afterwards. You don’t want a loose fit, so wrap the tape around the full length of the neck leaving about 2 fingers of space between the collar and neck.