Measure the circumference of your dog’s neck (A) by placing a flexible tape measure around the middle of his neck. The tape measure should be tight enough, but not restrict your dog. Leave approximately one finger’s width between the tape measure and your dog's neck. 

Because the specifications for adjusting our various collars usually overlap slightly, you do not necessarily have to use the first or last hole to guarantee an optimal fit. Should the circumference of the neck of your dog be at the upper end of the measurements specified then you can alternatively choose the next larger size. This is especially recommended for dogs that are still growing.

It should be noted that when considering the range of adjustments the first value relates to the smallest and the second value to the largest adjustment possible.