Calculators
Heat Index Calculator
Calculate heat index and feels-like temperature from air temperature and humidity using Celsius or Fahrenheit.
Weather Calculator
Heat Index Calculator
Calculate the heat index, also called feels-like temperature, from air temperature and relative humidity. Use Celsius or Fahrenheit and check the estimated heat risk level.
Weather inputs
Enter the air temperature and relative humidity. Higher humidity can make hot weather feel much hotter because sweat evaporates more slowly.
Quick examples
Heat index result
Heat index estimates how hot the weather feels when humidity is included.
Feels like
38.7°C
Estimated heat index
Heat index in both units
38.7°C / 101.6°F
Converted result
Air temperature
32°C / 89.6°F
Input temperature converted
Feels hotter by
6.7°C
Heat index minus air temperature
Heat risk level
Extreme caution
Heat-related discomfort is possible. Drink water and take breaks.
Heat index guide
80–89°F
Caution
90–102°F
Extreme caution
103–124°F
Danger
125°F+
Extreme danger
This calculator is for general planning only. Actual heat stress can also depend on sun exposure, wind, clothing, age, health, hydration, activity level, and how long you stay outside.
How to use the heat index calculator
Enter the current air temperature and relative humidity. The calculator estimates the heat index, which is the temperature your body may feel under humid conditions.
Heat index is most useful in hot and humid weather. When humidity is high, sweat evaporates more slowly, so the body has a harder time cooling itself.
Use this result as a general guide for outdoor work, sports, travel, school activities, and daily weather planning.
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What this heat index calculator helps you estimate
This heat index calculator helps estimate how hot the weather feels when humidity is included.
Heat index is useful because humid air can make it harder for sweat to evaporate, which can make the body feel hotter than the actual air temperature.
The calculator can be used for outdoor work, sports, travel planning, school activities, and daily weather decisions.
It supports both Celsius and Fahrenheit so users around the world can calculate feels-like temperature in their preferred unit.
The result is an estimate only. Actual heat stress can also depend on sun exposure, wind, clothing, hydration, health, and activity level.
Common uses for a heat index calculator
- Calculating feels-like temperature
- Checking heat risk before outdoor activity
- Planning sports, travel, or outdoor work
- Comparing Celsius and Fahrenheit heat index
- Understanding how humidity affects hot weather
Common heat index examples
How this heat index calculator works
Enter the air temperature in Celsius or Fahrenheit.
Enter the relative humidity percentage.
The calculator estimates the heat index, also called feels-like temperature.
The result shows the heat index in Celsius and Fahrenheit plus a general heat risk level.
Frequently Asked Questions
What is heat index?
Heat index is an estimate of how hot the weather feels when air temperature and humidity are combined.
Why does humidity make it feel hotter?
High humidity slows sweat evaporation, making it harder for the body to cool itself.
Can I use Celsius in this calculator?
Yes. You can calculate heat index using Celsius or Fahrenheit, and the result is shown in both units.
Is heat index the same as actual temperature?
No. Actual temperature measures the air temperature, while heat index estimates how hot it feels when humidity is included.
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