We have created the following guide for collar widths, but please consider the strength and size of your dog:  16mm is suitable for most miniature breeds and puppies;  19mm is suitable for most dog breeds, and is a 'standard' collar width;  25mm is suitable for larger or fluffier dogs, or for a 'chunky' look to ensure the collar stands out. We do not reccomend this size for very small dogs as the hardware can be heavy on their necks;  38mm is extremely chunky and perfect for very fluffy or large breed dogs;  Hound collars are specifically designed for sighthounds and long-necked dogs.  For leads:  16mm is suitable for miniature - small breeds and puppies;  19mm is suitable for small - medium dogs, or dogs which are not prone to pulling;  25mm is suitable for medium - large breed dogs.  If your dog is prone to pulling, or is extremely strong, please contact us before placing your order.