Even on a mild 70 °F (21 °C) day, a car’s interior can exceed 100 °F (38 °C) within 30 minutes. Opening the windows a little makes almost no difference. Children’s bodies heat up three to five times faster than adults’ – never leave a child or pet in a car.
How to use the Car Heat Calculator
- Outside temperature
- Minutes parked in the sun
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the outside temperature and the time the car is parked.
Inputs explained
| Field | What to enter |
|---|---|
| Outside temperature | Units: °C, °F |
| Minutes parked in the sun | A number |
What each result means
- Estimated temperature inside the car = [Outside temperature] + interp([Minutes parked in the sun], 0, 10, 0, 19, 29, 34, 38, 41, 43, 45, 47, 49)÷1.8
- Rise over the outside temperature = [Estimated temperature inside the car] – [Outside temperature]
Example values
How the main result changes when Outside temperature changes and everything else stays at the example values above:
| Outside temperature (°C) | Estimated temperature inside the car (°C) |
|---|---|
| 12.5 | 31 |
| 18.75 | 38 |
| 25 | 44 |
| 31.25 | 50 |
| 37.5 | 56 |
| 50 | 69 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Interior temperature ≈ outside temperature + rise over time
Typical rise: +19 °F (11 °C) in 10 min, +29 °F (16 °C) in 20 min, +34 °F (19 °C) in 30 min, +43 °F (24 °C) in 60 min
Worked example
Inputs — Outside temperature: 25 °C; Minutes parked in the sun: 30.
Results — Estimated temperature inside the car = 44 °C; Rise over the outside temperature = 19 °C.
Key terms
- Heatstroke
- Life-threatening rise in body temperature.
Frequently asked questions
How fast does a car heat up?
About 80% of the rise happens in the first 30 minutes.
Does cracking the windows help?
Hardly at all.
What should I do if I see a child or pet in a hot car?
Call emergency services immediately.