Heat Index Calculator
Calculate the heat index from temperature and humidity.
Quick answer: enter your details below and click Calculate Heat Index — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
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How to use
- Enter your values in the fields provided.
- Click Calculate Heat Index.
- Read the result and adjust an input if you want a different outcome.
About this tool
Humid air feels hotter than dry air at the same temperature. Enter temperature in Fahrenheit and relative humidity and this tool calculates the heat index with the standard Rothfusz formula. Below about 80 Fahrenheit it simply returns the temperature, since the formula is not meant for cooler air.
Frequently asked questions
What do I enter to get a result?
Fill in every field with your own numbers or choices, then run the tool. Empty number fields count as zero, so check them before you trust the output.
Can I reuse this result elsewhere?
Yes. The result is calculated in your browser from the values you entered, so you can copy the numbers into your own notes or plan.