Standard, Medium, Mini Size is measured to the top of the shoulder blades (withers) while standing squarely on a level surface. STANDARD: 21" TO 24" The "Ideal" size for a standard is 21 to 24 inches. Weight range tends to be 40 to 65 pounds. MEDIUM: 17" TO 20" The "Ideal" size for a medium 17 to 20 inches. Weight range tends to be 20 to 40 pounds. MINIATURE: 13" TO 16" The "Ideal" size for a miniature is 13 to 16 inches. Weight range tends to be 13 to 20 pounds. Most new puppy owners are interested in projecting how big their pup will be. The unofficial formula to guess at a dog's final weight is: At 6 weeks of age multiply the weight by 5 and add 5 pounds. At 4 months of age, double the weight and add 10 pounds for Standard size, 5 pounds for Medium size and 3 pounds for mini size. Of course ~ Only Mother Nature knows for sure!