To measure the width of your dog"s foot, place the foot on a piece of paper and press down on the top of the foot, mimicking how the foot spreads when the dog"s walking. Compare this to the boot sizes. the foot should be smaller than the boot size.Mark the left and the right side of the foot on the paper and measure the distance between the marks. Compare this to the boot sizes. The width of the foot should be smaller than the boot size. For example, if the foot width is 2 1/2 inches, order an Small at 2 3/4 inches.