Heat Index Calculator
HI = −42.379 + 2.049T + 10.143R − 0.225TR − 0.00684T² − 0.0548R² + 0.00123T²R + 0.000853TR² − 0.00000199T²R²Using the NOAA formula: HI≈100°F
Free online tool
Heat Index Calculator
Enter the air temperature in Fahrenheit and relative humidity percentage.
Instant calculation
Heat Index Calculator
Enter the air temperature in Fahrenheit and relative humidity percentage.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter temperature
Type the air temperature in degrees Fahrenheit.
- 02
Enter humidity
Type the relative humidity percentage.
- 03
See heat index
Calculate to see the apparent temperature.
The formula
How this calculation works
NOAA heat index formula. Valid for temperatures 80°F+ and humidity 40%+.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
90°F at 60% humidity — heat index?
Using the NOAA formula: HI≈100°F≈ 100°F (feels like)Common questions
Questions about this calculation
What is the Heat Index Calculator?
The Heat Index Calculator helps you calculate the heat index (feels-like temperature) from temperature and humidity. Enter your values and select Calculate to get an instant result.
How is the result calculated?
NOAA heat index formula. Valid for temperatures 80°F+ and humidity 40%+.
Can you show an example?
Example: 90°F at 60% humidity — heat index? — ≈ 100°F (feels like).
Is my data saved when I use the Heat Index Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Heat Index Calculator free to use?
Yes. The Heat Index Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
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