Why parked cars heat up so fast
A parked car acts like a greenhouse: sunlight passes through the glass, warms the interior surfaces, and the resulting heat is trapped inside, causing the cabin temperature to rise quickly and level off after roughly 30-60 minutes.
The formula
This calculator uses a curve fitted to widely cited vehicle-heating research (based on data popularized by studies from San Jose State University), modeled as: Temperature Rise = 45°F × (1 − e^(−0.047 × minutes)). This approximates real measured data such as roughly +19°F after 10 minutes, +29°F after 20 minutes, and +43°F after an hour, before leveling off near a maximum rise of about 45°F. Interior Temperature = Outside Temperature + Temperature Rise.
- Cars heat up fastest in the first 15-30 minutes
- Cracking a window has been shown to make little practical difference
This is an estimate for general educational and safety-awareness purposes only, based on averaged research data; actual temperatures vary by vehicle, sun exposure, and color. Never leave a child, pet, or anyone vulnerable to heat alone in a parked car, even briefly.