Heat Index Calculator by Top Librarians

Heat Index Formula:

\[ HI = -42.379 + 2.04901523T + 10.14333127RH - 0.22475541T \times RH \] \[ - 0.00683783T^2 - 0.05481717RH^2 + 0.00122874T^2 \times RH \] \[ + 0.00085282T \times RH^2 - 0.00000199T^2 \times RH^2 \]

Heat Index (°F):

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1. What is a Heat Index Calculator?

Definition: This calculator estimates the heat index (apparent temperature) based on air temperature and relative humidity using the Rothfusz regression equation.

Purpose: It helps assess how hot it feels when humidity is factored with air temperature, important for health and safety in hot weather.

2. How Does the Calculator Work?

The calculator uses the Rothfusz regression equation:

\[ HI = -42.379 + 2.04901523T + 10.14333127RH - 0.22475541T \times RH \] \[ - 0.00683783T^2 - 0.05481717RH^2 + 0.00122874T^2 \times RH \] \[ + 0.00085282T \times RH^2 - 0.00000199T^2 \times RH^2 \]

Where:

\( HI \) — Heat Index (°F)
\( T \) — Temperature (°F)
\( RH \) — Relative Humidity (%)

Explanation: This complex equation models how the human body perceives temperature when humidity affects the cooling efficiency of perspiration.

3. Importance of Heat Index

Details: The heat index helps prevent heat-related illnesses by indicating when conditions become dangerous for outdoor activities.

4. Using the Calculator

Tips: Enter temperature in °F (must be above 0°F) and relative humidity as percentage (0-100%). The calculator works best for temperatures above 80°F.

5. Frequently Asked Questions (FAQ)

Q1: What is considered a dangerous heat index?
A: Caution is advised above 90°F, extreme caution above 103°F, and dangerous above 125°F.

Q2: Why does humidity make it feel hotter?
A: High humidity reduces sweat evaporation, the body's primary cooling mechanism.

Q3: Does this work for temperatures below 80°F?
A: The equation is most accurate above 80°F. Below this, simple temperature is usually sufficient.

Q4: What adjustments are needed for direct sunlight?
A: Full sunshine can increase heat index values by up to 15°F.

Q5: How does wind affect heat index?
A: This calculator assumes light wind (about 6 mph). Higher winds can make it feel cooler.