Heat Index Calculator - Free, Instant, In Your Browser
Enter the temperature in Fahrenheit (80°F or higher) and relative humidity to calculate the heat index.
How to use Heat Index Calculator
- 1Enter the required date(s) and details above.
- 2Click Calculate - Heat Index Calculator runs instantly, right in your browser.
- 3Read your result below.
Your file is processed in your browser and is never uploaded.
Frequently Asked Questions
What's the formula?
Calculated via the Rothfusz regression, the official US National Weather Service heat index formula, valid for temperatures of 80°F and above.
Is my data sent to a server?
No - everything runs entirely in your browser with JavaScript. Nothing is uploaded.