Estimate cabin-air heating in full sun using an approximate 0–60 minute reference table. This cannot predict heatstroke or a safe waiting time. Never leave children, disabled adults or pets in parked vehicles.

Illustrative full-sun cabin-air estimate for 70–95°F outside and 0–60 minutes. Never leave children, disabled adults or pets in parked vehicles. This cannot establish a safe waiting time.

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Internal Car Temperature Formula

This calculator adds a temperature rise interpolated from the Jan Null estimate table. The table covers outside air temperatures of 70–95°F and times of 0–60 minutes.

Tᵢ = Tₐ + R(t)
  • Where T_i is the internal car temperature (°F)
  • T_a is the ambient temperature (°F)
  • t is the time in full sun (0–60 minutes); R(t) is the interpolated Fahrenheit rise

Add the interpolated rise to outside temperature: at 0, 10, 20, 30, 40, 50 and 60 minutes, the reference rises are 0, 19, 29, 34, 38, 41 and 43°F. Between adjacent points, use straight-line interpolation. These are approximate cabin-air estimates, not universal vehicle predictions.

What is an Internal Car Temperature?

Definition:

Internal car temperature typically refers to the temperature inside a vehicle's cabin, which can become significantly higher than the outside temperature when exposed to direct sunlight.

How to Calculate Internal Car Temperature?

Example Problem:

The following example outlines the steps and information needed to calculate the internal car temperature.

First, determine the ambient temperature. In this example, the ambient temperature is 75°F.

Next, determine the time in the sun. In this example, the car was exposed to sunlight for 30 minutes.

Finally, calculate the internal car temperature using the formula above:

T_i = T_a + R(t)

T_i = 75 + R(30)

T_i = 75 + 34

T_i = 109°F

FAQ

What factors can affect the internal car temperature?

The internal car temperature can be influenced by factors such as ambient temperature, duration of sunlight exposure, vehicle color, and window tinting. External conditions like air circulation and humidity may also impact the rate at which the interior heats up.

How can I reduce the internal car temperature during sunny days?

Shade, sunshades and other vehicle conditions may affect heat buildup, but they do not establish safe occupancy. NHTSA warns never to leave a child unattended in a vehicle for any length of time; shade or opening windows does little to protect them. The National Weather Service also warns against leaving disabled adults or pets in parked vehicles.

Can this calculator provide precise internal temperature predictions?

No. It interpolates an approximate reference table and starts cabin air at outside air temperature. Actual starting temperature, vehicle and weather conditions may differ. The inverse reports only a table-based time to a selected cabin-air temperature, within a 0–43°F rise and 0–60 minutes. An out-of-range target does not mean a real car cannot reach it. Cabin-air temperature is not core body temperature, and this tool cannot estimate time to injury or a safe waiting time.