What the tool does, how to run it, and what to expect from the result.
Humid air slows sweat evaporation, so the body feels hotter than the thermometer says. The NWS uses the Rothfusz regression with small corrections for very low and very high humidity. 90°F with 70% relative humidity feels like 106°F, in the Danger band (103-124°F) where heat cramps and heat exhaustion are likely.
Short, plain-language definitions for the formats and settings above.
A quick way to understand who this helps, what it solves, and where it connects next.
Students, lab workers, electricians and engineers who want the formula and the answer.
Using the heat index calculator without installing anything or signing up.
Short answers for the questions people usually have before trying a utility like this.
NWS levels: 80-90°F caution, 90-103°F extreme caution, 103-124°F danger, 125°F and above extreme danger.
No. It assumes shade and a light wind. Full sun can add up to 15°F to the felt temperature.
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Enter your numbers and the result updates live in your browser. Nothing is uploaded and no server is used.
Calculations run locally in your browser; nothing is uploaded.