Pratico

Heat Index Calculator

Unità:

Temperature (°C)

Relative Humidity (%)

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Detailed Guide Coming Soon

We're working on a comprehensive educational guide for the Heat Index Calculator in your language. The content below is shown in English.

Cos'è Heat Index Calculator?

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The heat index (apparent temperature or "feels like" temperature) combines air temperature and relative humidity to show how hot it actually feels, since humidity impairs the body's ability to cool through sweating.

Calkulon makes complex calculations simple — built for students and everyday problem-solvers.

Formula

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f(x)HI ≈ −42.379 + 2.04901523×T + 10.14333127×RH − 0.22475541×T×RH (°F, %)

Leggenda delle variabili

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Simbolo	Nome	Unità	Descrizione
HI	Heat Index	°F or °C	—
T	Air temperature	°F	—
RH	Relative humidity	%	—

Come Heat Index Calculator

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1Heat index = Rothfusz regression equation with 9 terms
2Simplified: HI ≈ −42.379 + 2.049T + 10.143RH − ... (°F)
3Only meaningful when T > 27°C (80°F) and RH > 40%
4Heat stroke risk when HI > 40°C (103°F)

Esempi risolti

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Esempio 1

Dato:Temperature 35°C, humidity 70%

Risultato:Heat index ≈ 44°C (feels like 44°C due to high humidity)

Applicazioni pratiche

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Weather advisory issuance

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Athletic event safety (water breaks)

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Occupational health (outdoor workers)

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Public health warnings

Heat Index Risk Levels

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Heat Index	Risk level	Health effects
27–32°C	Caution	Fatigue with prolonged activity
33–39°C	Extreme caution	Cramps, heat exhaustion possible
40–51°C	Danger	Heat exhaustion likely
> 51°C	Extreme danger	Heat stroke imminent

Domande frequenti

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Why is heat index different from temperature?

Heat index accounts for body's inability to cool via sweat evaporation. High humidity + heat = dangerous.

What heat index is dangerous?

>90°F: heat cramps likely. >103°F: heat exhaustion. >125°F: heat stroke risk high.

Can I use wind chill in summer?

No. Wind chill applies to cold. Wind actually increases heat stress by reducing cooling. Use heat index instead.

Riferimenti

›Heat index — NWS

Formula-verified for precision

Reviewed October 2026

Our methodology

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Heat Index Calculator