It may seem to you measure your dog´s neck easy but its very hard for some people to do it right. Collars are made custom so its very important to measure it properly. If you dont do it, it can happen that you will recieve too big or too small collar. You have to realise that every mentioned sizes are sizes of dog´s neck, not final size of collar. For best measuring is good tailoring meter. When you measure dog´s neck it is good to put two fingers under meter. Best place for measuring dog´s neck is in the middle of his neck.