When the correct size is chosen, the fit should allow the collar to sit comfortably - not so loose that it can slip over your dog's head and not so tight that they cannot breathe!
Our sizes are designed with overlap between them. Each collar has five holes for the buckle prong. If you have a puppy and the required length falls between the end of one size and the beginning of the next, we suggest that you choose the bigger size as they will grow into it.
If you have an existing collar then measuring the length of that will be the easiest way to select the size. If you don't, measure your dog's neck against the skin using a tape measure and add 1 cm wriggle room. The additional 1 cm should allow you to slip one or two fingers underneath the collar once it is on your dog.
For example, if the length you need is 35 cm (including the extra 1 cm) then you have a choice of two sizes. If you choose Size 2 then you will do the collar up on the second to last hole. If you choose Size 3 then you will do the collar up on the second hole