What is the Hot Car Temperature Calculator?
This tool estimates how hot the interior of a parked, closed car becomes over time when left in the sun. The inside of a vehicle heats up far faster than most people expect — even on a mild day, the cabin can become deadly within minutes. The calculator uses a logarithmic model based on published vehicle-heating studies to show how the interior temperature climbs above the outside air temperature.
How to use it
Enter the current outside temperature, choose Fahrenheit or Celsius, and enter how many minutes the car has been parked. The calculator returns the estimated interior temperature and the temperature rise above ambient. Use it to understand just how quickly a vehicle becomes dangerous.
The formula explained
The heat rise follows a logarithmic curve because the car warms quickly at first, then more slowly as it approaches a peak. We model the rise (in °F) as $$\Delta T = 12.4 \times \ln\!\left(t + 1\right)$$ where \(t\) is minutes. This produces roughly +19°F after 10 minutes, +34°F after 30 minutes, and +43°F after 60 minutes — values consistent with research from pediatric and meteorological studies. The inside temperature is then simply the outside temperature plus this rise (rise is converted to °C when Celsius is selected).
Worked example
Suppose it is 85°F outside and a car has been parked for 30 minutes. \(\Delta T = 12.4 \times \ln(31) = 12.4 \times 3.434 \approx 42.6\)°F... wait, the model gives $$\Delta T = 12.4 \times \ln(30 + 1) = 12.4 \times 3.434 \approx 42.6\,\text{°F}$$ Adding to 85°F gives about 128°F inside — well into the lethal range. The longer a car sits, the hotter and more dangerous it becomes.
FAQ
Is this exact? No. Actual interior temperature depends on sun angle, color, windows, and ventilation. Treat results as an awareness estimate, not a safety guarantee.
At what temperature is it dangerous? Children's bodies overheat 3–5× faster than adults. Heatstroke risk begins around a core temperature of 104°F (40°C), which a hot cabin can cause very quickly.
Does cracking a window help? Studies show leaving windows slightly open has minimal effect on the peak temperature. Never leave a child or pet in a parked car, even briefly.
