The short answer: about double the temperature outside, and it gets there faster than almost anyone expects.
On a 30°C day — an ordinary Australian summer afternoon, not a heatwave — the inside of a parked car can reach around 50°C. On a genuinely hot day the RSPCA has recorded interiors reaching up to 73°C. Most of that rise happens in the first ten minutes.
The part that catches people out
It isn't the peak temperature. It's the speed.
A car's interior can climb more than 20°C in under ten minutes, even on a mild day. That's the window in which people think they're being reasonable — ducking into the shop, paying for fuel, grabbing one thing. The RSPCA's campaign on this is called Just Six Minutes, and the name is the argument: six minutes is enough to kill a dog.
Nobody plans to leave their dog for twenty minutes. They plan to leave them for five, and then there's a queue.
Shade and a cracked window don't solve it
This is the most common assumption and it is the wrong one. Parking in the shade slows the rise a little. Leaving windows open a few centimetres slows it a little. Neither brings the interior anywhere near safe, and shade moves as the sun does — the shaded spot you parked in at 1pm is in full sun by 1:30.
Why dogs come off worse than we would
People sweat. Dogs mostly don't. They shed heat by panting, which works by evaporating moisture from the mouth and airways — and that stops working once the air around them is hot and humid enough. In a sealed car, the air a panting dog breathes out is the air it breathes back in.
Flat-faced breeds — pugs, French bulldogs, boxers — have less airway to work with and struggle sooner. So do older dogs, overweight dogs, and dogs with heart or breathing conditions. But heatstroke is not limited to them. A healthy young dog in a hot car is in trouble just the same.
What heatstroke looks like
Heavy, frantic panting. Drooling more than usual. Bright red gums and tongue. Unsteadiness, stumbling, or a dog that seems confused. Vomiting or diarrhoea. In severe cases, collapse or seizures.
If you see this, it's an emergency, not a wait-and-see. Move the dog somewhere cool, wet them with cool — not ice-cold — water, offer small amounts to drink if they're conscious, and get to a vet immediately. Call ahead so the clinic is ready.
If you see a dog alone in a car
Note the registration and the location. Check whether the dog is showing any of the signs above. If the shop is nearby, ask staff to page the owner.
If the dog appears to be in distress, call the police on 000 or your state RSPCA cruelty line. They can attend and they have powers you don't. Breaking a window carries legal consequences that vary by state, so make the call first and let them advise you.
The honest part
We sell things for dogs in cars. So it would be convenient for us to end this by suggesting one of them helps.
It doesn't. Nothing we sell — or that anyone sells — makes a parked car safe for a dog. Not a cooling mat, not a ventilated seat, not a window shade. Those things make a moving car with the aircon on more comfortable. They do nothing about a sealed metal box in the sun.
The only thing that works is not leaving the dog there. If the errand can't be done with the dog beside you, the dog stays home. That's the whole method.
Figures in this article come from RSPCA Australia and RSPCA Queensland. If you're unsure whether it's too hot to travel with your dog at all, your vet is a better source than any website, including this one.
