In order to know which model you will need for your dog, you will need to know his or her weight, length and height from paw pad to shoulder.
B. Measure up to the tip of the nose with the dog's head extended as shown
C. Measure from the top of the shoulder to the floor or their paw pads as shown
The best way to measure your dog is using a sewing tape measure, or use a string and then measure your lengths (see pictures below).
You will also need to weigh your dog. This can be accomplished by having your dog stand on a scale, or you can hold your dog and weigh both of you, then just weigh yourself and subtract.
Enter your dog's length, weight and height to shoulder. Your suggested model will be shown. (click here for metric)