Hot Car Temperature Calculator
Estimate how hot a parked car gets in the sun. Enter the outdoor temperature in Fahrenheit or Celsius and how many minutes the car has been closed to see the interior temperature and its danger level.
Example: with Outside temperature 90 · Temperature unit Fahrenheit (°F) · Minutes parked 30 → Interior temperature: 124 °F.
- Temperature rise+34 °F
- Danger levelVery dangerous — heatstroke likely; never leave anyone inside
Computed by the calculator below using its default values. Change any input to see your own numbers.
Interior temperature rise follows the McLaren, Null & Quraishi (2005) study: about +19°F after 10 minutes and +43°F after an hour, largely regardless of how warm it is outside.
Why a parked car turns into an oven
Sunlight pours in through the glass and heats the seats, dash, and carpet. Those surfaces re-radiate heat that the closed cabin traps, so the temperature climbs fast at first, then levels off as the car loses heat about as quickly as it gains it. The striking finding from the research is that the rise depends mostly on time, not on how hot it started.
That is why a 70°F day is still dangerous: the interior can gain 40 degrees or more within an hour, pushing past 110°F. The car does not need a heat wave to become deadly — it just needs sun and a closed cabin.
Children and pets heat up faster
A small body warms far more quickly than an adult's, and children's temperature regulation is less developed. A child left in a hot car can reach heatstroke — a core temperature of 104°F — long before the cabin hits its peak, and around 107°F is often fatal. Pets, unable to sweat, are at similar risk.
Treat every number here as a warning, not a countdown. If you see a child or animal alone in a hot car, act immediately.
How it’s calculated
Interior temperature = outside temperature + heat rise. The rise is read from the McLaren/Null 2005 elapsed-time curve (0, 10, 20, 30, 40, 50, 60 minutes maps to 0, 19, 29, 34, 38, 41, 43 °F) with linear interpolation between points and a plateau at +43°F beyond one hour. The rise is nearly independent of the starting temperature. A Celsius rise is the Fahrenheit rise × 5/9.
An estimate for a typical car in direct sun with the windows up; cracking a window changes little. This is not a safety margin — never leave a child, adult, or pet in a parked car, even briefly, and call emergency services if you find one.
Interior heat over time (90°F day)
| Time parked | Temp rise | Interior at 90°F outside |
|---|---|---|
| 10 min | +19°F | 109°F |
| 20 min | +29°F | 119°F |
| 30 min | +34°F | 124°F |
| 40 min | +38°F | 128°F |
| 50 min | +41°F | 131°F |
| 60 min | +43°F | 133°F |
Temperature rise from McLaren C, Null J, Quraishi J. Heat Stress From Enclosed Vehicles. Pediatrics 2005;116(1):e109. Interior = outside temperature + rise.
Common mistakes
- Assuming a mild day is safe — the interior still climbs 40°F or more in an hour, so 70°F outside can pass 110°F inside.
- Believing a cracked window prevents the rise; studies found it makes little difference.
- Thinking shade or a cloudy start removes the danger; the rise is largely independent of the outside temperature.
- Treating the interior number as a countdown — a child's core heats much faster, so harm can come well before the peak.
Frequently asked questions
How hot does a car get in the sun?
Interior temperature is roughly the outside temperature plus a time-based rise: about +19°F after 10 minutes and +43°F after an hour. On a 90°F day the cabin can pass 130°F within an hour.
Does cracking a window keep a car cool?
Barely. Research by McLaren, Null and Quraishi found that leaving windows slightly open had little effect on how hot the interior became. Do not rely on it.
How quickly is a hot car dangerous for a child or pet?
Fast. A child's core temperature can reach heatstroke levels within minutes on a warm day, and pets that cannot sweat are at similar risk. There is no safe amount of time.
What should I do if I see a child or pet alone in a hot car?
Call 911 or your local emergency number immediately and stay until help arrives. This tool is only an estimate — treat any enclosed-car situation as an emergency and defer to first responders.
Does this work in Celsius?
Yes. Choose Celsius and the outside temperature and result are shown in °C; the heat rise is converted from the published Fahrenheit curve.