The Leuchtie is placed on the dog as a closed ring and it is only necessary to open it for initial activation

and battery replacement.

So the size of the head is the measurement you need - NOT THE NECK MEASUREMENT.

Re-size an adjustable collar so that you can place it over the dogs head and pull it back off again without it being too tight and uncomfortable for the dog.


Now  measure the INSIDE of the adjusted collar with a flexible tape measure as precisely as possible. 

Alternatively, create a string of strip of paper inside the adjusted collar and measure this.

The select the nearest size Leuchtie, remembering that there is only a very little amount of "give" in the Leuchtie.