How to measure for collar size
You will need:
1) Something to measure with: A seamstress' or tailor's type tape measure is best, but if you don't have one you can use a ribbon or a piece of string and a yardstick or ruler -- mark the measurement on the ribbon, and then use the yardstick or ruler to measure it.
2) Treats: They improve cooperation :)
3) Pen and paper: Prevents the necessity of re-measuring when you forget the numbers.
4) A friend: Helpful if your dog is a squirmer, or to keep your little one from jumping off the tabletop while you write down the measurements.
5) The dog :)
Use the tape or string to measure around the dog's neck where his or her collar is then add 2 inches.
A properly fitting collar should allow you to slip two fingers easily underneath, between the collar and the dog's neck. Even after he or she is full gown, be sure to check the fit of your dog's collar periodically, as changes in weight, and even the growth of a heavier winter coat can affect the fit. Leather and some other collar materials can stretch or shrink over time, especially if they get wet. A properly fitted collar is imperative, as a too-tight collar can cause serious injury, and a too-loose collar can easily slip off over your dog's head.
Write down each measurement, and then measure a second time just to be sure. I can do returns and exchanges but would rather not to prevent the possibility of skin diseases or parasites being transmitted to other pets. It is better to measure twice than be sorry!
When you are all done, be sure to give your dog an extra treat for being such a good model!