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Heat Index Calculator

Estimate apparent heat from air temperature and relative humidity.

Heat Index Calculator Inputs

Results computed instantly — your data never leaves your device.

Heat Index Calculator Results

Real-Time

Heat index

113.1 °F

Applicability

NOAA formula range used

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How to Use the Heat Index Calculator

  1. 1

    Enter air temperature in °F.

  2. 2

    Enter relative humidity.

  3. 3

    Review heat index when the formula range applies.

  4. 4

    Follow current heat advisories and hydration guidance from local authorities.

Formula & Mathematical Basis

The Rothfusz regression estimates heat index from temperature and relative humidity using its published polynomial coefficients.

Variable Key

T

Air temperature in °F

RH

Relative humidity in percent

📝 The widget applies the polynomial in a common hot/humid range and otherwise reports air temperature as not applicable.

Step-by-Step Examples

1

Hot and humid conditions

Scenario: 95°F and 60% relative humidity.

  1. 1.Confirm hot/humid applicability.
  2. 2.Substitute T=95 and RH=60.
  3. 3.Evaluate the regression terms.
  4. 4.Review approximately 113.1°F.
✅ Heat index is approximately 113.1°F.

Practical Use Cases

  • Explain how humidity changes perceived heat.
  • Compare hot-weather scenarios with consistent units.

Common Pitfalls

  • Confusing heat index with actual air temperature.
  • Using relative humidity as a fraction instead of percent.
  • Ignoring official heat warnings and individual vulnerability.

Frequently Asked Questions

Does it predict health outcomes?

No; it is an apparent-temperature estimate, not a medical prediction.

What should I do during extreme heat?

Follow current local authority guidance and seek help for concerning symptoms.

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