The short answer: sooner than you think. The long answer depends on three things, and none of them is the number of degrees alone.
What really matters
Size. Small dogs lose heat faster because they have a lot of surface area in proportion to their body mass. A Chihuahua gets cold at temperatures where a Bernese Mountain Dog is only just waking up.
Coat. An undercoat insulates. Dogs without one, such as sighthounds, dachshunds, boxers, many terriers and almost all dogs with a short clip, are out there underdressed at five degrees.
Age and health. Puppies, seniors and dogs with joint problems need warmth not as a comfort, but as protection. Cold makes stiff joints stiffer.
The honest rule of thumb
- Above 10 degrees: no dog needs a coat. Really, none.
- 5 to 10 degrees: small, slim and short-haired dogs on longer walks, older dogs in general.
- 0 to 5 degrees: anything without an undercoat should be dressed, as soon as it's more than a quick wee.
- Below 0: now wet and wind count too. A wet dog loses many times more heat.
| Temperature | Who needs a coat |
|---|---|
| Above 10 degrees | no dog |
| 5 to 10 degrees | small, slim and short-haired dogs on longer walks, older dogs in general |
| 0 to 5 degrees | all dogs without an undercoat, as soon as it's more than a quick wee |
| Below 0 degrees | all sensitive dogs, and now wet and wind count too |
How to tell your dog is cold
Shivering is the late sign, not the first. Before that come: lifted paws, a tucked tail, a hunched back, and that hesitant stop at the door that looks like stubbornness and isn't.
If any of that sounds familiar, take a look at our jackets and coats. No dog needs five of them. One that fits is enough.
When it's rainy, wet comes on top of the cold. What else matters then is covered in our raincoat guide.