Parked-Car Heat Timeline
See how a parked car’s interior temperature climbs minute by minute in Phoenix heat, built from published research on vehicle heating rather than from estimates.
Jump to a temperature
- 10 minutes
- 94 °F
- 30 minutes
- 109 °F
- 60 minutes
- 118 °F
- Share done in 30 min
Interior after one hour
+43 °F in an hour
At 75 °F outside, the published table puts the interior at about 94 °F after ten minutes, 109 °F after thirty, and 118 °F after an hour. 79% of the hour's rise is done in the first half hour, so the car is most of the way there before anyone has finished an errand.
Interior temperature, minute by minute
Air at 75 °F outside. The curve runs from the moment the doors shut to the sixty-minute mark, where the published table stops climbing.
Drawn from the table published by Jan Null (San José State), which is itself calculated from McLaren, Null & Quinn, Pediatrics 2005. The dotted line is the outside air; the distance above it is the rise.
Publisher’s note
No figure on this page supports leaving a person or an animal in a parked car at any temperature above 70 °F, for any length of time. The tool exists so the number is understood, not so it can be used to justify a short trip.
The number is a calculation, and the calculation is public
There is an honest problem at the centre of this tool. The question people ask is "how hot does it get in a parked car in Phoenix in July", and the honest answer is that nobody has measured it. The measurement that exists was made in Fremont, California, across sixteen cloud-free days in the summer of 2002, with the outside air between 72 and 96 °F. Above 96 °F, the instrument stops and the evidence stops with it.
What this tool draws instead is the published table that grew out of that study. Jan Null, one of the study's own authors, took the measured rate and extended it into a table of interior temperatures from 70 to 110 °F outside at five-minute steps. His table carries two labels a reader should notice: at the bottom, Calculated from Published Study, and on the row past one hour, Estimated. This page repeats both labels and stops at sixty minutes, where the labelled data stops.
What the measurement itself found
The study's findings are worth stating on their own, because they are the part that is measured rather than derived:
- The interior rose an average of 3.2 °F every five minutes.
- 80% of the total rise happened inside the first thirty minutes. The car is mostly cooked before an errand is finished.
- The interior reached 117 °F even on the coolest day of the study, when the outside air was 72 °F.
- The average total rise was about 41 °F, with individual days ranging from 28 to 49 °F, and the interior stopped climbing at 60 minutes.
- Cracking the windows made no significant difference to either the rate or the maximum.
That last finding is why this page does not offer a "windows cracked" toggle. It would be a control that promises to change the answer when the study says the answer does not change.
Why the rise is the same regardless of how hot it is outside
The unglamorous reason a parked car heats so predictably is that it is a greenhouse with a large thermal mass. Shortwave sunlight passes through the glass, lands on the seats, the dash and the carpet, and comes back as longwave infrared, which the glass does not let out. The energy that arrives has nowhere to go, so the interior air warms until the surfaces and the air are in equilibrium.
The published table happens to show the same rise (within a degree) in every ambient column, which is why the left column of this page's data is a single row rather than a grid. What changes with the outside air is where the curve starts, not how far it climbs. That is a slightly strange result and it is the one the data gives.
How to use it
Set the slider to the temperature you expect at the car. The readout gives you the interior an hour later; the three figures beneath the slider give you ten, thirty and sixty minutes, because the interesting part is the early slope. At 100 °F outside the table puts the interior above 110 °F within five minutes and above 129 °F by twenty, which is the same figure Maricopa County publishes on its own pet-safety page. Two independent documents arriving at 129 °F is the closest thing here to a cross-check.
The chart is drawn on the published five-minute grid, so every point on it is a number somebody published rather than a number this page invented between them. Use the temperature buttons to move between the four outside temperatures people actually ask about, or the slider if yours is in between.
What this tool will not do
It will not tell you your car is fine. It cannot see your interior colour, your window tint, whether you parked in the shade or on asphalt, or whether you left a sunshade up. All of those change the number and none of them are in the study. And it will not give you a safe duration, because the shape of the curve does not contain one: the interior is above the danger line before the first published data point at five minutes on any summer afternoon.
- McLaren C, Null J, Quinn J. "Heat Stress From Enclosed Vehicles." Pediatrics, July 2005; 116(1):e109–e112
The measured rate an enclosed car heats: 3.2 °F of rise every five minutes, 80% of the total rise inside the first thirty minutes, a maximum at sixty minutes, and 117 °F reached even on the coolest day of the study.
- Jan Null, CCM: Department of Meteorology and Climate Science, San José State University. "Vehicle Interior Temperature Rise vs. Elapsed Time"
The interior temperature at every five-minute step from 70 to 110 °F outside. The table labels itself "Calculated from Published Study", and this page repeats that label rather than presenting the figures as measurements.
- Maricopa County: "Protect Your Pet From the Heat" (adapted from the Arizona Humane Society): via Maricopa County pet heat guidance
Independent corroboration from a county public-health document: at 100 °F outside, the county states the inside of a car reaches 129 °F in twenty minutes, which is the same figure as the derived table.
Every figure this tool uses was read from the source named above on 10 October 2026. Anything still waiting on a check is listed in the site's data notes rather than shown here as if it were settled.
Before you rely on this
This tool works from climate normals and published guidance, not from live weather. It describes a typical day for the month or date you chose, which is useful for planning and useless as a forecast.
- The measured study ran at 72 to 96 °F outside. There is no measured interior dataset above 96 °F, so the 105 and 110 °F columns this tool draws are extrapolation from the study’s rate, not observations. At a Phoenix July afternoon of 110 °F the tool is furthest from its evidence, and that is exactly when people ask it.
- The study used one vehicle: a dark-blue 2000 Honda Accord with a medium-grey interior and no tint, measured over sixteen cloud-free days in Fremont, California. It does not describe your car. A lighter interior, a sunshade, tint, or a covered garage will all move the number, and this tool cannot tell you by how much.
- The sensor sat fifteen inches above the rear seat, in shade. A dashboard or a child seat in direct sun will read higher than the figure shown here; the footwells will read lower.
- Values between the published five-degree columns and between the published five-minute steps are linearly interpolated. Entering 108 °F puts you between the measured 105 and 110 columns.
- The derived table stops at sixty minutes. The published row beyond one hour is labelled "Estimated" by its own author, so this tool stops where the labelled data stops rather than drawing an estimated tail.
- This is not a forecast. It describes a car with the engine off, the windows closed, and the sun on it.