Dogs have different sizes and weights. There is no one collar suits all situation. Tiny dogs weights from 2kg and can be as small as a cat. Small dogs weight from 5kg, medium size dogs weight from 12kg, large dogs weight from 25kg and extra large dogs can weight up to 100kg. The weight is also not only judgement to the collar as dogs have different shape and temperament. For example, miniature dachshund is a tiny small dog but it has a bigger neck than some small or even medium size dogs. A e collar designed for small dog will be also suitable for this tiny dog. Jack Russell is a small dog but it is high energy and head strong. Citronella spray collar may work on lots of small dogs but not for Jack Russell. We try to keep example or list of suitable dog breeds in each product categories, but if you cannot find the breed of your dog in the categories, please contact us on 1800 300 364 or 07 5559 9100 for advise.