Medium-sized dogs are defined by their weight, height, and length, and generally weigh between 20 and 60 pounds. However, the way people define medium-sized dogs can vary, and some organizations break down dog sizes into detailed groups, including extra-small, small, small-medium, medium, medium-large, large, extra-large, and giant. In general, small dog breeds tend to go up to about 20 pounds, and large dog breeds begin around 60 pounds. So anything in the middle could be considered a medium-sized dog.

Medium-sized dogs are the best of both worlds, possessing some traits of both small and large dogs, and their maintenance also generally falls somewhere in the middle. They are a popular choice for families, as they are not too big and not too small, and there is a huge selection of breeds to choose from. Some of the most popular medium-sized dog breeds include the American Staffordshire Terrier, Australian Cattle Dog, Australian Shepherd, Basenji, and Basset Hound.

Examples of small to medium-sized dog breeds include the Standard American Eskimo Dog, American Water Spaniel, Basenji, Beagle, Bedlington Terrier, Cesky Terrier, Cocker Spaniel (both American and English), French Bulldog, Dandie Dinmont Terrier, German Pinscher, Miniature Bull Terrier, Norwegian Buhund, Shetland Sheepdog, and Swedish Vallhund.

In summary, medium-sized dogs weigh between 20 and 60 pounds and are a popular choice for families. They are not too big and not too small, and there is a wide variety of breeds to choose from.