๐ฅต Heat Index Calculator
Enter the air temperature (ยฐC) and relative humidity (%) to calculate the "feels like" heat index using the formula adopted by the US National Weather Service (NWS), along with a caution level. Useful as a quick reference during hot, humid weather.
How to use
- Enter the current air temperature (ยฐC).
- Enter the current relative humidity (%) โ the feels-like temperature and caution level are calculated automatically.
FAQ
What is the heat index?
It's a measure of how hot it actually feels to the human body, combining air temperature and humidity. High humidity slows sweat evaporation, making it feel hotter than the air temperature alone would suggest.
Is this the same as WBGT (Wet Bulb Globe Temperature)?
No, they're different indices. WBGT also factors in solar radiation and wind speed, and is the standard used in Japan for heat-stroke prevention guidance. The Heat Index calculated here is a simpler US-originated index based only on temperature and humidity.
What are the caution level thresholds based on?
This tool uses the US National Weather Service's Fahrenheit thresholds (80ยฐF, 90ยฐF, 103ยฐF, 125ยฐF), converted to Celsius. These differ from Japan's WBGT-based heat-stroke guidance, so treat the result as a general reference.