Heat Index Calculator
Calculate "feels like" temperature combining heat and humidity using the NOAA / Rothfusz regression. Heat index applies above 80°F.
Inputs
Heat index
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In Celsius
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Heat index effect
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Risk level
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Actual conditions
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About Heat Index Calculator
Why humidity matters
Your body cools through sweat evaporation. High humidity slows evaporation, trapping heat. At 100% humidity, sweat can no longer cool you — heat index can be 30°F above air temp.
Wet-bulb temperature
A more rigorous measure used in athletics and industry. A wet-bulb above 95°F is dangerous because sweating can\u2019t cool you below it. Above 100°F: lethal within hours.
When heat index understates risk
In direct sun, add ~15°F. Heat index assumes shade. Athletes, kids, elderly, and those on certain medications feel heat earlier than the index suggests.