Measure the the length from the tip of the claw to the point the back of the foot meets the ground (the back of the dog's pad). Measure the width at the widest point. We suggest having your dog stand on a piece of paper, tracing around his foot, and then measuring the outline on the paper.
IMPORTANT NOTE: The chart below is furnished by the manufacturer, but sizes seem to run very small. We recommend ordering one full size larger.