To measure the nek of your dog you need a flexibele measuring tape. Note: do not measure too tight!
A = Blue
B = Yellow
For a regular dogcollar, measure at A
If you want a half check dogcollar you can also measure at A but I also need the size of the widest part of your dog's head. 

For a anti-thick collar you also measure at A but it will hang at B

You are responsible for providing the correct size. If for some reason you are unable to measure the neck size of your dog, please send Special Dog Design a message and I can still help you further.