Heat Index Calculator
Estimates human-perceived heat based on NOAA NWS standards.
Safe
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Risk Level: --
What is the Heat Index?
The Heat Index (HI) is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. It is widely known as the "feels-like" temperature.
The Formula
NOAA uses the Rothfusz regression. For temperatures ≥ 80°F:
HI = -42.379 + 2.049*T + 10.14*RH - 0.224*T*RH ...
When to use it?
- To assess heat stroke risk during summer activities.
- For occupational safety planning in warehouses or outdoors (though WBGT is preferred for direct sun).
Step-by-Step Example
If T = 90°F and RH = 70%:
- The air temperature is 90°F.
- High humidity prevents sweat evaporation.
- The calculation yields a heat index of 105°F.
- This falls into the Danger category.
Frequently Asked Questions
Caution begins at 80°F. Extreme Caution at 90°F. Danger at 103°F. Heat
stroke is imminent above 125°F.
No. Heat Index assumes shady conditions. Direct sunlight can increase the
values by up to 15°F.