1. What is the Heat Index?

The Heat Index (HI) is a measure that combines air temperature and relative humidity to determine the human-perceived equivalent temperature. It represents how hot it feels when humidity is factored in with the actual air temperature.

2. How Does the Calculator Work?

The calculator uses the Rothfusz regression equation:

Where:

• \( T \) — Temperature in degrees Fahrenheit
• \( R \) — Relative humidity percentage
• \( c_1 \) to \( c_9 \) — Regression coefficients

Explanation: The equation models how the body perceives temperature when humidity affects its ability to cool through perspiration.

3. Importance of Heat Index

Details: The heat index is crucial for assessing heat-related health risks. Higher values indicate increased danger of heat exhaustion, heat stroke, and other heat-related illnesses.

4. Using the Calculator

Tips: Enter temperature in °F (must be ≥80°F) and relative humidity in % (must be ≥40%). The calculation is only valid within these ranges.

5. Frequently Asked Questions (FAQ)

Q1: Why is heat index higher than actual temperature?
A: High humidity reduces the body's ability to cool through sweat evaporation, making the temperature feel hotter than it actually is.

Q2: What are dangerous heat index levels?
A: 80-90°F: Caution; 90-103°F: Extreme Caution; 103-124°F: Danger; 125°F+: Extreme Danger.

Q3: Does wind affect heat index?
A: The standard heat index assumes light wind (5-6 mph). Higher winds can make it feel cooler by increasing evaporation.

Q4: Why doesn't the calculator work below 80°F?
A: The equation was designed for hot conditions where humidity significantly impacts perceived temperature.

Q5: How is heat index different from "feels like" temperature?
A: Heat index specifically accounts for humidity, while "feels like" may also incorporate wind chill in cold conditions.