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Hot Car Calculator

Created by Łukasz Białek, MD and Dominik Czernia, PhD
Reviewed by Bogna Szyk and Jack Bowater
Based on research by
Ebi, K. L., Capon, A., Berry, P., Broderick, C., de Dear, R., Havenith, G., Honda, Y., Kovats, R. S., Ma, W., Malik, A., Morris, N. B., Nybo, L., Seneviratne, S. I., Vanos, J., Jay, O. Hot weather and heat extremes: health risks; Lancet (London, England); August 2021See 3 more sources
Grundstein, A., Meentemeyer, V., Dowd, J. Maximum vehicle cabin temperatures under different meteorological conditions; International journal of biometeorology; 2009Dadour, I. R., Almanjahie, I., Fowkes, N. D., Keady, G., Vijayan, K. Temperature variations in a parked vehicle; Forensic science international; 2011Grundstein, A., Dowd, J., Meentemeyer, V. Quantifying the heat-related hazard for children in motor vehicles; Bulletin of the American Meteorological Society; 2010
Last updated: Jan 18, 2024

Picture this; it's a hot summer's day; you got up early to go to the park and, having spent a few hours there, are ready to drive home. You open your car and immediately regret your decision - your car is now roughly the temperature of the sun! The seats have become molten lava, and don't even think about touching the steering wheel. Many experiments have shown that even on a cooler summer day, temperatures inside a closed vehicle can quickly exceed 125 °F (about 52 °C). It seems that cars are built to turn into hot ovens, and, as you will see later, we mean it literally! All your stuff, including electronic devices, medicine, or food, could end up getting permanently damaged at these temperatures.

But, most importantly, by leaving pets or people in the parked car, you put their lives at grave risk. Some statistics estimate that about 40 children die per year due to being left in hot cars, and more than half of them are under two years old. 2018 and 2019 were the deadliest years in the past 20 years in the US: 53 children died in hot cars in 2018, and 52 children died in 2019. Take a moment and explore this topic a little more with the hot car calculator so that you become well aware of heat hazards!

Child hyperthermia deaths statistics.

Heatstroke hazards in closed vehicles

Global warming is a fact, and we now have to deal with the health consequences of increased temperatures. We should pay special attention to babies, children, pregnant women, and the elderly as these individuals are the most vulnerable in hot weather, according to an article from the Department of Health of the Government of Western Australia publication Health effects of heat – who is most at risk?

Jan Null is a Certified Consulting Meteorologist that continuously monitors reports on child vehicular heatstroke deaths in the U.S.. It turns out that between 1998 and August 2019, 849 children died from vehicular heatstroke, and many more have been put in a life-threatening state. It is worth noting that only 18.9% of these kids were left knowingly by a caregiver. Most of them (54%) were just forgotten or gained access on their own (26.3%). Below you will find some descriptions of death certificates from Jan Null's site. Don't these situations sound like something that can happen to anyone? Are you sure you will never let this happen to your children?

  • 13th November 2019, Walnut in California: 73 °F (23 °C) - "Boy's father arrived at his work in the shopping center, forgetting to take his child to daycare. Daycare workers later phoned the father, and he realized the boy was still in the car. The boy was discovered after about six hours inside the SUV by the father. When deputies arrived, they found him performing CPR on his son." - the 18-month-old boy died.
  • 25th April 2020, Tomball in Texas: 78 °F (25.5 °C): - "The 4-year-old child managed to get out of the house on his own and into the vehicle. The family didn't notice anything. They found him in a hot vehicle Saturday." - the 4-year-old boy died.
  • 28th May 2020, Clewiston in Florida: 90 °F (32 °C) - "A woman heard the ambulance and police sirens and saw first responders heading to her neighbors. She didn't know what had happened. Two days later, she learned that a baby had been left in a car for an unknown amount of time. The woman said: How can you forget somebody like that?" - the 10-month-old girl died.
  • 6th June 2020, Tulsa in Oklahoma: 94 °F (34.5 °C) - "A man drove to a convenience store about noon Saturday with his two children in a truck. After shopping, he returned home, passed out, and was asleep for 4 - 5 hours. After waking up, he couldn't locate the children. He found them on the floorboard of his truck. Later on, it was found that the children left the car with their dad but then got into the truck on their own when the man was asleep." - the 3-year-old boy and 4-year-old girl died.

There are many more examples of similar tragedies. The danger of a hot car is real and should never be underestimated, even if there is "only" around 70 °F (20 °C), such as in the first case. Death may come in any warmer place on Earth. Australia is no exception. Kidsafe Victoria, the Child Accident Prevention Foundation of Australia, reports that over 5,000 children have been rescued after being left in a car. The Ambulance Victoria responded 1587 callouts for people locked in cars (mostly children) between 1st September 2017 and 31st August 2018, and this is only one state! NRMA (The National Roads and Motorists' Association in Australia) warns that more than 50% of parents are still leaving their children unattended in vehicles.

In November 2019, a major tragedy happened in Queensland when a young Australian mother unconsciously left her two children to die (one and two years old) inside the hot car.

If you want to educate yourself on how to keep your child safe, you should check the Hot Car Safety Tips for Parents, prepared by certified pediatrician Vincent Iannelli which can be found at Make it a habit to always think of your children and where they are, and prevent them from getting into a vehicle by themselves.

Child hyperthermia deaths statistics.

Interior temperatures - turning a car into an oven

You can find many works that consider the severity of leaving children and pets in a stationary vehicle on a hot summer day. All of them unanimously agree the temperature in the cabin of the car can become 70 °F (or 40 °C in SI units temperature difference) hotter than the ambient temperature outside, even on relatively cool and cloudy days. Andrew Grundstein from the University of Georgia is a world-renown expert in the field of climate and human health, with a large number of comprehensive publications. In one of them, he thoroughly studied the Maximum vehicle cabin temperatures under different meteorological conditions, and developed two simple predictive models (based on solar radiation and sky cloud cover) that can be used interchangeably.

To understand how dangerous increased cabin temperatures could be, let's take a look at the terminology of the National Weather Service (NWS), an organization in the United States that provides weather forecasts and warnings. The NWS glossary issues two warnings depending on the heat index value (a combination of air temperature and relative humidity - more details are in the heat index calculator):

  • Heat advisory when the heat index is between 105 °F (40.5 °C) and 115 °F (46 °C) for less than 3 hours. At this point, people can be affected by heat, often leading to an increased number of emergency room visits.
  • Excessive heat warning is issued if the time spent in the 105 °F - 115 °F (40.5 °C - 46 °C) range is longer than 3 hours or the heat index is greater than 115 °F (46 °C) for any period of time. This is when people are in severe danger, and mortality begins to increase rapidly.

Are you still not sure about this threat? Just watch the following video demonstrating of a car turning into the oven, literally. Australian chef Matt Moran overcooked a delicious lamb loin in a little over an hour and a half using only his car. Now, try to imagine that there is a kid or a dog trapped inside that vehicle!

Temperature vs. time - do open windows help?

So, why does the interior of a car get hotter than its surroundings? In simple terms, it is because of the greenhouse effect occurring in the vehicle, the same effect that is the main cause of global warming. As you can learn from the wavelength to energy calculator, shorter wavelengths are of higher energy so that they can pass through matter more easily. Car windows act similarly to the Earth's atmosphere; they are almost transparent to light radiation (which has short wavelengths) but prevent thermal radiation (long wavelengths) from leaving. Therefore, solar radiation goes through the windows and heats the interior elements of the car, e.g., the dashboard, seats, or floor. Those elements then emit thermal radiation, but it is blocked by the car windows when it tries to escape the car. This traps the heat radiation in the vehicle, causing the cabin temperature to increase dramatically.

Greenhouse effect.

This greenhouse effect was analyzed experimentally during summer by Andrew Grundstein in the paper Quantifying the Heat-Related Hazard for Children in Motor Vehicles. With the collected data and simulations, he provided a representative table of temperature change rates inside a vehicle on days with various ambient air temperatures. Moreover, the Royal Automobile Club of Queensland Limited (RACQ) conducted several tests to measure the interior temperatures of parked cars in a Car Survey. They concluded:

  • There is no safe situation to leave children unattended in a vehicle, even for a short amount of time.
  • Interior of the cars with dark paint color heats up faster compared to light colors, but only slightly.
  • Sunshades and window tinting may slightly slow the rate of temperature rise, but final interior temperatures remain almost the same.
  • Leaving the partly open windows may reduce the temperature in a car.

Be aware that the last point doesn't mean it is safe to leave a living thing inside a parked vehicle. The rate of increase in the cabin's temperature is reduced, but it is still quite rapid. Use the hot car calculator to find out for yourself! So, leaving your windows open does not increase safety over time and isn't great for security.

Heat illness

When you spend some time in a high temperature, your body's thermoregulatory efficiency decreases, and your body temperature rises. We call this state hyperthermia; a body absorbs more heat than it dissipates. It is hazardous when body temperature is higher than 40 °C (104 °F). Such a situation is known medically as heat illness, which may proceed as:

  • Heatstroke (the most dangerous);
  • Heat cramps;
  • Heat rash;
  • Heat syncope;
  • And others.

Typical symptoms of heatstroke include dizziness, headaches, confusion, sleepiness, seizures, and the absence of sweating. Treating heatstroke is focused on rapid mechanical cooling of the patient and intravenous dosages of fluid. Patients also receive drugs to treat seizures, as well as painkillers. Heatstroke is a serious medical condition that can result in many complications and has a mortality rate of about 40%.

It's difficult to predict when heatstroke will strike because it involves many factors like a person's age, weight, and health conditions. Babies and young children are especially susceptible to high temperatures and, consequently, to hyperthermia. Physicians at Children’s Hospital say that a child’s body can heat up three to five times faster than an adult’s, and when the body’s temperature reaches 104 degrees, the internal organs begin to shut down.

Why are children more vulnerable to hyperthermia? There are many reasons for that; here is the list of the most important ones according to UpToDate:

  • Heat production – Children produce more metabolic heat per kilogram of body weight because they have a higher basal metabolic rate than adults.

  • Body surface area – Younger children have a higher body surface area (BSA) to mass ratio, resulting in a greater rate of heat absorption in hot environments. You can find body surface area from weight and height using the BSA calculator.

  • Blood circulation – Children have a smaller absolute blood volume, which limits the potential of blood-borne heat transfer from the body core to the body surface, where heat dissipates. You can also find blood volume from weight and height with our dedicated blood volume calculator.

  • Sweat production – Children have a lower rate of sweating than adults as a result of a lower sweat rate per gland and a higher body temperature at which they begin sweating.

  • Fluid replenishment – Children are more likely to inadequately replenish fluid losses during prolonged exercise if not appropriately supervised.

  • Acclimatization – Children achieve adaptations to a hot environment more slowly than adults

In the research paper, Evaluating the impact of solar radiation on pediatric heat balance within enclosed, hot vehicles, the authors assessed the core temperature rise of a toddler using specific heat capacity of a 13.4 kg (29.5 lbs) boy. They concluded that the core temperature of an infant enclosed in a car might change from 36.8 °C (98.2 °F) to a lethal 40 °C (104 °F) in only one hour!

Find out more about heat in our specific heat calculator!

Picture of sleeping child.

It is worth noting that some regions have Good Samaritan Laws, giving you immunity if you act to protect the life of a child inside of a hot vehicle. If you ever see a child left unattended in a car, don't hesitate and use force (e.g., break a window) to save a child from heatstroke. You will avoid any legal consequences. This law may differ from place to place around the world, so be sure to check whether this applies in your country!

How to use the hot car calculator?

The hot car calculator is based on a few studies already mentioned in this article. It allows you to estimate a car's temperature and a child's expected body temperature over time. If you still have any doubts about using it, follow the instructions below:

  1. Type in the outside air temperature - our calculator uses a model that is most accurate on warm days when the air temperature ranges from about 68 °F (20 °C) to 122 °F (50 °C).
  2. Select the way you wish to estimate maximum car interior temperature; it will determine the next steps. You can use calculations based on either solar radiation or sky-cloud coverage.
  • If you chose cloud cover - decide how much of the sky is covered in clouds or assess it in percentages in the advanced mode (clear sky - 0%, and overcast - 100%).
  • If you chose solar radiation - select a day of the year and one of the capitals or countries around the world. We will calculate solar radiation theoretically. For more precise estimations, you can type in the latitude of your town by hand in advanced mode (the latitude of a particular place can be easily found on the Internet).
  1. Decide whether your car color is light or dark and if your car has either closed or partly open windows.
  2. That's it! You can now scroll down to see two interactive graphs:
  • The blue curve shows the change in the car's internal air temperature.
  • The yellow-red curve represents the estimation of a 2-year-old boy's body temperature.

Each of the curves has some special points highlighted above the graph. These include the National Weather Service (NWS) heat warning systems on the blue curve and health consequences of increased human body temperature on the yellow-red curve.

Don't forget about pets!

Dogs, cats, and other animals can't sweat like humans. They can only pant to lower their body temperature. However, panting with hot air gives no relief at all, and the risk of heatstroke rises very rapidly. Don't leave your pet in a car "just for a minute". What if your business takes a little longer, or you forget about it entirely? People for the Ethical Treatment of Animals (PETA) state that animals can sustain brain damage or even die from heatstroke in just 15 minutes. Unlike child deaths, these tragedies are often ignored by the media, but, in fact, thousands of animals suffer the same painful fate every year. If you own an animal, think twice before taking your pet for a ride that includes stops and errands.

Picture of enclosed dog in car.

Unfortunately, if you see a locked pet, you cannot always act similarly to the case of a child and Good Samaritan Laws. The vehicle's owner might sue you for the destruction of personal property. Instead, follow the advice of personal injury lawyers Hupy and Abraham: call 911 (or the corresponding emergency number in your country), try to find the owner of the vehicle and shade the animal through the window until authorities arrive.


How hot does a car get in the sun?

Even when the outside temperature is 68 °F (20 °C), the temperature inside a car parked in the sun under a clear sky can shoot up to 118.2 °F (47.9 °C) in just one hour! By three hours, the inside temperatures may reach 140.8 °F (60.4 °C)!

Are black cars hotter?

Several tests run by the Royal Automobile Club of Queensland Limited (RACQ) concluded that the interior of darker cars heat up faster than lighter cars. However, this does not mean that lighter color paints are safe, because the difference between light and dark paint colors is small.

What temperature is too hot for a dog in a car?

There is no safe temperature for you to leave your pets and children in cars parked in the sun — even if the outside temperature is a cool 68 °F (20 °C), the temperature inside the car can soar to 118.2 °F (47.9 °C) in just one hour!

What should I do when I park my car in the sun?

A car parked in the sun can quickly turn into an oven! Ensure that you:

  1. Do NOT leave children, pets, elderly people, or pregnant women in the car. They are the most vulnerable to heat stroke.

  2. Do NOT leave behind water, food, alcohol, and medicine, especially in plastic containers.

  3. Do NOT forget any electronic devices like laptops and phones inside the car. High temperatures can permanently damage your devices.

  4. Do NOT leave bike tires or anything that can expand and blow up due to heat.

  5. Do NOT leave any chocolate or crayons if you don't want them to melt and damage your upholstery.

What temperature can you leave a dog in the car?

It is never safe to leave kids and dogs in cars in the sun. In just one hour, the temperature inside a car can rise to 118.2 °F (47.9 °C), even if it is a cool 68 °F (20 °C) day!

What temperature is safe to leave a dog in the car?

Leaving children and dogs in cars in the sun is never a safe idea. Even on a chilly 68 °F (20 °C) day, the temperature inside an automobile can reach 118.2 °F (47.9 °C) in just one hour!

Łukasz Białek, MD and Dominik Czernia, PhD
Outside temperature
Calculations based on
cloud cover
Cloud sky coverage
few clouds (20%)
Temperature vs. time
Car color
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