The overall circumference measurement of your dog's noggin at the largest point is the best determination of size, because if you choose a size too large, the muffs won't seal well against his head, and you lose all the sound-reducing properties you were shooting for. 

The circumference is the measurement that would create a circle by going across the top of the dog's head, over the ears, and under the chin.

Your dog's weight is also a good indicator of which size to choose.


Size Max Width Max Height
XS

1.5"
3.81 cm

1.625"
4.12 cm

Small

1.75"
4.44 cm

1.75"
4.44 cm

Medium

2.5"
6.35 cm

2.5"
6.35 cm

Large

3.25"
8.25 cm

3.25"
8.25 cm

XL

4"
10.16 cm

4"
10.16 cm