Car Heat Calculator — Temperature Inside a Parked Car
Estimate the interior temperature of a car parked in the sun: enter the outside temperature and parking time to see how hot the cabin gets, with a danger-level rating to protect children, pets and vulnerable passengers.
Temperature unit
°C
min
Approximate car interior temperature after the specified time in the sun
- 1
Temperature rise exponent
−30 ÷ 18 = -1.667 - 2
Temperature rise (°C)
24 × (1 − e^-1.667) = 19.47Exponential approach to the empirical +24 °C plateau (Jan Null 2018 model). - 3
Interior temperature
25 + 19.47 = 44.5
How does this calculator work?
A car parked in direct sun can heat up by ~10 °C in 10 minutes and ~19 °C in 30 minutes above the outside temperature, modelled as ΔT = 24 × (1 − e^(−t/18)). At 25 °C outside, the interior can exceed 44 °C in 30 minutes — life-threatening for children, infants, and pets. Never leave vulnerable people or animals in a parked car.
Formula
How this is calculated
A parked car in sunlight acts like a greenhouse: shortwave solar radiation passes through the glass and heats the interior surfaces, which then re-emit longwave infrared that cannot escape through the glass. The temperature inside rises rapidly — most of the increase occurs within the first 30 minutes. Research by meteorologist Jan Null (San Jose State University, updated 2018) measured temperature rises in a variety of vehicles under typical sunny conditions and found average interior rises of roughly +10 °C in 10 minutes, +19 °C in 30 minutes, and up to +24 °C after about an hour.
This calculator models that rise with an exponential approach to a plateau: ΔT = 24 °C × (1 − e^(−t/18)), where t is time in minutes and 18 minutes is the empirical time constant. The outside temperature is then added to get the absolute interior temperature. The model is an approximation — actual values can be higher or lower depending on vehicle colour (dark absorbs more), window tinting, sun angle, cloud cover, and whether windows are cracked.
The critical safety implication is that even mild outdoor temperatures can produce lethal interior conditions within minutes. At an outside temperature of 22 °C (72 °F), the interior can reach 43 °C (109 °F) in 30 minutes — well above the threshold for heatstroke in young children. A child's body temperature rises three to five times faster than an adult's. Cracking a window has been shown to have minimal effect on the rate of temperature rise.
Frequently asked questions
Heatstroke in children begins when core body temperature reaches 40 °C (104 °F). Children's bodies heat up three to five times faster than adults'. As a rule, never leave a child in a parked car — even with windows cracked, even for a few minutes. At 25 °C outside, the interior can exceed dangerous levels in under 20 minutes.
Research has consistently shown that cracking windows has little effect on the rate of interior temperature rise. The difference between fully closed and cracked windows is typically only 1–2 °C. Active ventilation (engine running with air conditioning) is the only reliable way to keep the interior cool.
No — this is an empirical estimate based on averaged measurements across a range of vehicles. Dark-coloured cars with black interiors can heat more than the model predicts; silver or white cars in partial shade may be cooler. The model gives a safe-side estimate for an average car under full sun. Always err on the side of caution.
Also known as
TG we-Calculate Editorial Team. (2026). Car Heat Calculator — Temperature Inside a Parked Car [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/car-heat-calculator
TG we-Calculate Editorial Team. "Car Heat Calculator — Temperature Inside a Parked Car." TG we-Calculate. 2026. https://we-calculate.com/calculator/car-heat-calculator.
TG we-Calculate Editorial Team, "Car Heat Calculator — Temperature Inside a Parked Car," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/car-heat-calculator
@misc{wecalculate_car_heat_calculator, title = {Car Heat Calculator — Temperature Inside a Parked Car}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/car-heat-calculator}}, year = {2026}, note = {TG we-Calculate} }
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