1. What is Heat Index?

Definition: Heat Index (HI) is a measure that combines air temperature and relative humidity to determine the human-perceived equivalent temperature.

Purpose: It indicates how hot it feels when relative humidity is factored with the actual air temperature, helping assess heat-related risks.

2. How is Heat Index Calculated?

The calculator uses the Rothfusz regression formula:

Where:

• \( HI \) — Heat Index (°F)
• \( T \) — Temperature (°F)
• \( R \) — Relative Humidity (%)
• \( c_1 \) to \( c_9 \) — Regression coefficients

Note: This formula is only valid when temperature is 80°F or higher. Additional adjustments are made for extreme humidity conditions.

3. Importance of Heat Index

Details: The Heat Index is crucial for:

• Assessing heat stress and heat-related illness risks
• Planning outdoor activities and work schedules
• Issuing heat advisories and warnings
• Understanding apparent temperature effects

4. Using the Calculator

Tips:

• Enter temperature in °F (must be ≥ 80°F for valid calculation)
• Enter relative humidity as a percentage (0-100%)
• The calculator automatically applies necessary adjustments

5. Frequently Asked Questions (FAQ)

Q1: Why does humidity affect how hot it feels?
A: High humidity reduces the body's ability to cool through sweat evaporation, making the temperature feel hotter than it actually is.

Q2: What's considered a dangerous heat index?
A: Heat indices above 103°F are dangerous, and above 125°F are extremely hazardous with high risk of heat stroke.

Q3: Why is there a minimum temperature of 80°F?
A: The formula was developed specifically for warmer conditions where humidity significantly impacts perceived temperature.

Q4: How accurate is the heat index calculation?
A: The formula is accurate to within ±1.3°F when compared with experimental data, assuming proper measurements.

Q5: Does wind speed affect heat index?
A: The standard heat index doesn't account for wind. Wind chill factor is used for cold temperatures with wind.