How Cold Is Too Cold for Dogs, Exactly?

Your dog's cold tolerance depends on several factors, including their size, hair, health status, age and breed. Generally speaking, healthy adult large breed dogs with medium and long hair tend to have a higher cold tolerance than puppies, older dogs, small breeds, dogs with short hair or dogs with preexisting health problems.

Dog Breeds Who Love the Cold
Arctic breeds who have traditionally lived in cold temperatures — such as malamutes, huskies, Keeshonden and Saint Bernards — actually enjoy and prefer being outdoors in freezing and subfreezing temperatures. As long as they have an insulated, windproof and waterproof shelter (and access to fresh, unfrozen water), healthy Arctic breed adults who are accustomed to the cold can be outside in temperatures well below zero for as long as they want.

Dog Breeds Who Can Handle a Short Time in the Cold
Medium and large warm weather breeds — such as Dalmatians, boxers, Rottweilers and border collies — can be outside in temperatures down to zero if they're exercising heavily (i.e., running or playing in the snow) for up to 30 minutes. These breeds could potentially stay out even longer if they wear a coat. However, it's important to supervise your dog at all times and bring them inside immediately if they exhibit any signs of frostbite or hypothermia. If they're just standing around or relieving themselves, they're usually OK outside without a coat for five to 10 minutes.
Dogs in Winter: Keep Your Dog Safe in Cold Weather | Hill's Pet
Dog Breeds Who Can't Handle the Cold
Small warm weather breeds — such as Chihuahuas, Yorkies and Italian greyhounds — share a different answer to the question of how cold is too cold for dogs: These dogs are intolerant of freezing temperatures. Accordingly, they shouldn't spend longer than 10 to 15 minutes outdoors in temperatures between 10 and 32 degrees Fahrenheit (F), and they shouldn't spend any time outdoors in temperatures less than 10 degrees F. Some toy breeds may even refuse to urinate or defecate outside when it's cold or snowy. In these situations, it can be helpful to train your dog to eliminate on pee pads during the winter.

Puppies of all breeds are more sensitive to the cold than adults, and they can develop hypothermia and frostbite quickly. Monitor your puppy at all times when they're outdoors in freezing temperatures.