What is the Heat Index Calculator?
Calculate the heat index (“feels like” temperature) from air temperature and humidity. These physics and science calculators apply standard SI formulas with exact constants (such as g = 9.80665 m/s² and the 2019 SI definitions) for students, engineers and curious minds.
How to use the Heat Index Calculator
- Enter your air temperature, your relative humidity.
- Results update automatically as you type; you can also press Calculate.
- Read the output: heat index, in celsius.
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With air temperature = 90 °F, relative humidity = 60 %, the Heat Index Calculator returns heat index: 99.7 °F; in celsius: 37.6 °C.
Tips for better results
- Convert inputs into SI units first for the cleanest results.
- Idealized formulas ignore friction and air resistance unless stated.
- Use our unit converters to switch between metric and imperial results.
Frequently asked questions
What does the Heat Index Calculator do?
Calculate the heat index (“feels like” temperature) from air temperature and humidity.
How is it calculated?
The Heat Index Calculator uses this method: NWS Rothfusz regression (with low/high humidity adjustments).
Can you show an example?
With air temperature = 90 °F, relative humidity = 60 %, the Heat Index Calculator returns heat index: 99.7 °F; in celsius: 37.6 °C.
Is the Heat Index Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the Heat Index Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
Related tools
📬 Get new tools first — free
Join Taurang to hear about new calculators, converters and features. No spam; unsubscribe anytime.