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Heat Index Calculator

🌡️Heat Index Calculator

Best for T > 27°C / 80°F

40–100%

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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.

What is Heat Index Calculator?

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The heat index (feels-like temperature) combines air temperature and relative humidity to determine the apparent temperature. High humidity impairs the body's ability to cool itself through sweating, making hot conditions feel significantly hotter than the thermometer reads.

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How to Heat Index Calculator

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  1. 1Uses the Rothfusz regression equation (NWS, USA)
  2. 2Only applicable when temperature > 27°C (80°F) and humidity > 40%
  3. 3Below this threshold, the actual temperature is used directly
  4. 4HI = −42.379 + 2.04901523T + 10.14333127RH − 0.22475541TH − 0.00683783T² − 0.05481717RH² + ...

Worked Examples

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Example 1
Given:35°C (95°F), 70% humidity
Rezultatas:Feels like 51°C (124°F)

Extreme danger level

Example 2
Given:32°C (90°F), 50% humidity
Rezultatas:Feels like 38°C (100°F)

Caution — heat cramps possible

Heat Index Risk Categories (NWS)

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Heat Index (°F)CategoryRisk
80–90CautionFatigue possible with prolonged exposure
90–103Extreme CautionHeat cramps, heat exhaustion possible
103–124DangerHeat cramps/exhaustion likely, heat stroke possible
125+Extreme DangerHeat stroke highly likely
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Pro Tip

During heat advisories, stay hydrated (drink before you feel thirsty), avoid outdoor activity during peak hours (10 AM–4 PM), and check on elderly neighbours who are most vulnerable.

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Did you know?

The human body can only cool effectively when sweat evaporates. At 35°C with 100% humidity, sweat cannot evaporate at all — the body's cooling system effectively shuts down.

Mathematically verified
Reviewed October 2026
Our methodology

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