Because all collars are customised production they can not be exchanged or returned. So that the collars for your puppy will perfectly fit we need the following three measurements:
We need the head size so the collar fits over the head, the circumference behind the ears definites the size of the slip and the neck size specifies how tight or low the collar will fit.
Please note while taking the measure of the head size you have to take the widest part (including the ears).
Alternatively you can use a well-fitting collar and put a measuring tape around on the inside of the collar.
DON'T!!! put a measuring tape aorund on the outside of the collar and don't measure the length of the collar.