How to measure width:
Place dogs foot on paper and press on top to spread foot like when walking.
Mark the sides.
Width of foot should be smaller than the size of the boot.

Sizes:
Petite 1 1/4" width
XSmall 1 3/4" width
Small 2 1/4" width
Medium 2 3/4" width
Large 3 1/4" width
XLarge 4" width