Heat Index Calculator
Find the feels-like temperature from heat and humidity.
How hot it really feels
When humidity is high, sweat cannot evaporate efficiently, so a hot day feels even hotter. The heat index captures that by combining temperature and humidity into a single feels-like figure.
At 32°C and 70% humidity, it feels closer to 41°C. This calculator uses the National Weather Service formula, which applies to hot, humid conditions; in cooler or drier air the feels-like value is near the actual temperature.
Practical and private
It applies the NWS regression in your browser, so nothing you enter is uploaded.
Frequently Asked Questions
What is the heat index?
The feels-like temperature that combines air temperature and humidity, because sweat evaporates poorly in humid air, making it feel hotter.
When does it apply?
The formula is designed for hot, humid conditions — roughly above 27°C and 40% humidity. Below that, the feels-like temperature is close to the actual one.
What formula is used?
The US National Weather Service regression, computed in Fahrenheit and converted back to Celsius.
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