The determination of when the temperature is too cold for a dog is breed-specific. Some breeds of dogs withstand relatively extreme cold temperatures, while others lack that capability.
An initial step to protect a dog from harm caused by low temperatures is an appointment with a veterinarian. A veterinarian is able to advise to the weather tolerance of a particular breed of dog. In addition, a veterinarian examines a dog to determine if any conditions exist that might render a specific pet more vulnerable to negative effects from cold temperatures. Sweaters for dogs are not a fail safe way of protecting them from the cold. Dogs lose most of their heat through the pads on their feet.