1. What is a Heat Index Calculator?

Definition: This calculator computes the heat index (HI) based on current temperature and relative humidity measurements.

Purpose: The heat index indicates how hot it feels when relative humidity is factored with actual air temperature.

2. How Does the Calculator Work?

The calculator uses the Rothfusz regression formula:

Where:

• \( HI \) — Heat index (apparent temperature in °F)
• \( T \) — Ambient dry-bulb temperature (°F)
• \( R \) — Relative humidity (%)
• \( c_1 \) to \( c_9 \) — Empirical coefficients

Note: The formula is only valid when temperature is ≥80°F and relative humidity is between 0% and 100%.

3. Importance of Heat Index

Details: The heat index helps assess:

• Risk of heat-related illnesses
• Comfort levels in warm weather
• Necessity for cooling measures

4. Using the Calculator

Tips: Enter the current temperature (°F) and relative humidity (%). The calculator works best for temperatures above 80°F.

5. Frequently Asked Questions (FAQ)

Q1: Why doesn't the calculator work below 80°F?
A: The heat index formula is only scientifically validated for temperatures ≥80°F. Below this, humidity has minimal effect on perceived temperature.

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: How accurate is this calculator?
A: It uses the official NWS formula with accuracy of ±1.3°F when properly implemented.

Q4: Does this account for wind or sunshine?
A: No, the standard heat index assumes shade and light wind conditions. Full sunshine can increase perceived temperature by up to 15°F.

Q5: What's the highest possible heat index?
A: Theoretically unlimited, but the highest recorded was 178°F in Saudi Arabia (2003) with 108°F air temperature and 67% humidity.