About this tool
Find how hot it feels when humidity is combined with the air temperature.
The US National Weather Service method: a simple formula below 80 °F, otherwise the Rothfusz regression with adjustments for very dry or very humid air.
Formula: HI = −42.379 + 2.049T + 10.143RH − …
Example: Temperature = 35, Unit = °C, Relative humidity = 60 → Heat index (°F) = 113.1, Heat index (°C) = 45.1.
Assumes shade and light wind; direct sun can add up to about 8 °C. This is not medical advice.
Quick steps
- Enter your values — every field shows its unit.
- Press Calculate (or Try an example to see how it works).
- Read the results and copy them if you need them elsewhere.
The calculation runs in your browser. Nothing you type is sent to 1CLIK.
FAQ
How does the Heat Index Calculator work?
The US National Weather Service method: a simple formula below 80 °F, otherwise the Rothfusz regression with adjustments for very dry or very humid air.
What should I keep in mind?
Assumes shade and light wind; direct sun can add up to about 8 °C. This is not medical advice.
Is my data sent anywhere?
No. The numbers stay on your device; the page only shows the result.