Heat Index Calculator
Heat index combines air temperature and relative humidity into the "feels like" temperature your body actually experiences. Uses the National Weather Service algorithm (Steadman simple formula with the Rothfusz regression) and classifies the result into caution, extreme caution, danger and extreme danger zones.
TheCalculators — Heat Index Calculator
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Heat Index (Feels Like)
104.7 °F
≈ 40.4 °C · 92 °F actual at 60% RH
- Air Temperature
- 92 °F (33.3 °C)
- Relative Humidity
- 60%
- Heat Index
- 104.7 °F · 40.4 °C
- Humidity Burden
- +12.7 °F above actual
- Risk Level
- Danger
NWS heat danger zones
104.7 °F
Danger
NWS heat danger zones
The regression is calibrated for 80–115 °F. In direct sunshine the effective heat index can be up to 15 °F higher than in the shade. Drink water, seek shade, and never leave people or pets in parked cars.
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Formula
HI = −42.379 + 2.049T + 10.143R − 0.2248TR − 0.006838T² − 0.05482R² + 0.001229T²R + 0.0008528TR² − 0.00000199T²R² (T °F, R %)
Pro tips
- • Fans cool people, not rooms — they help only below ~95 °F.
- • Check the heat index, not the temperature, before scheduling outdoor work or practice.
FAQ
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