1. Measure the collar your dog is currently wearing.
If your dog currently has a collar that fits perfectly and you're just replacing it, you can simply use a ruler or tape measure to get an accurate measurement. Lay your dog's collar flat next to the ruler or tape measure and note where the measurement begins.
2. Use a soft tape to directly measure the dog's neck
If your dog is not currently wearing a collar or the collar it is currently using does not fit properly, you can only use a soft tape to measure the circumference of your dog's neck. The most accurate measurements are obtained when the dog is in a relaxed standing position. Gently wrap the tape measure snugly around your dog's neck, where the collar's head and tail meet, loosening it slightly to allow a little extra breathing room. Or when measuring, make the head and tail of the tape ruler overlap slightly to leave extra breathing space. The length of this overlapping section can vary depending on the size of the dog, the thickness of its fur, and even the amount of daily exercise, but it generally needs to be about 2 to 5 centimeters.
If your dog isn't used to this type of measurement, is a little irritable, or you're not sure your measurements are accurate, you can measure your dog's neck multiple times. If you get an approximate measurement every time, then the result is basically considered accurate.
3. Use a rope to measure
If you don't have a tape measure handy, you can cut a piece of string or even use shoelaces to measure your dog. Then, wrap it snugly around your dog's neck in the same manner as you would a tape measure, then relax it slightly to give it breathing room. You get the size of your dog's neck by pinching the area where the rope overlaps between your fingers and using a tape measure or ruler to measure the rope.
Something to note when using this method is that some ropes are elastic, such as shoelaces. Therefore, you need to be careful not to pull this type of elastic rope too hard when measuring, otherwise the measured data will be too small.