Heat Index Calculator

Calculate the apparent temperature from heat and humidity using the NWS heat index formula. Know your heat stroke risk before hot-weather hiking.

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Visualization

How It Works

The heat index combines air temperature and humidity to show how hot it actually feels. At 90F and 60% humidity, it feels like 100F. Above 105F heat index, heat stroke becomes likely with prolonged exertion. Hike early (before 10 AM) or late (after 4 PM) in hot weather. Drink before you're thirsty — by the time you feel thirst, you're already dehydrated.