🌡️ Heat Index & Real-Feel Calculator
Calculate the NOAA Heat Index ("feels like" temperature) from air temperature and relative humidity. View heat exhaustion danger categories.
Free No Signup Required Browser-Based
Must be 80°F (27°C) or higher
Apparent “Feels Like” Heat Index
103°F (39°C)
Extreme Caution
Heat cramps and heat exhaustion possible with prolonged exposure and activity.
How to Use Heat Index & Real-Feel Calculator
- Enter ambient air temperature in Fahrenheit (≥80°F)
- Input relative humidity percentage
- View the apparent feels-like temperature and heat danger classification
📖 Technical Encyclopedia & Standards Reference
Calculate the NOAA Heat Index ("feels like" temperature) from air temperature and relative humidity. View heat exhaustion danger categories. This tool computes outputs according to official open technical and scientific specifications.
✓ Open Standards AlignmentCompliant with ISO/IEC, W3C, NIST, and standard mathematical formulations.
✓ 100% Client-Side / SecureZero server logging. Computations execute entirely in your local browser sandbox.
Explore more formulas in our Tools Encyclopedia & Glossary →
Frequently Asked Questions
What is the Heat Index?
The Heat Index is a measure of how hot it really feels when relative humidity is factored in with actual air temperature, reflecting the body’s reduced ability to cool itself via sweat evaporation.
What temperature triggers the Heat Index formula?
The standard NOAA Rothfusz regression applies when ambient temperature is 80°F (27°C) or higher with relative humidity ≥ 40%.