# Heat Index Calculator

By factoring in the combination of temperature and humidity, the heat index calculator provides valuable insights and helps you make informed decisions when you need to assess the true level of heat stress.

## What is the Heat Index?

The heat index, also called apparent temperature, combines air temperature and humidity into a single "feels like" metric representing perceived warmth. The result gauges the total heat stress and risks.

For example, 90°F with extreme humidity has a much higher heat index and greater danger than 90°F with average moisture levels. Understanding true excess heat conditions allows you to take appropriate safety measures as you work and play outdoors.

## Why Calculate Heat Index?

Here are key reasons for tracking this vital health indicator:

 Goal Reason Assess risk Heat index directly indicates level of heat exposure dangers from temperatures and moisture Trigger alerts Compare index values against cautionary thresholds to prompt preventative safety breaks and hydration Quantify stress Allows communicating humidity's exponential impact on heat stress experienced Improve models Feed index data into forecasting systems to better predict heatwaves and guide emergency planning

Let's examine how heat index calculators derive these insights crucial for health and productivity.

## Using a Heat Index Calculator

Luckily heat index is easy to determine yourself:

1. Enter Temperature
• Typically in °F or °C from a thermometer
2. Input Humidity %
• Gathered from a hygrometer reading
3. Get Heat Index
• The calculator combines metrics into experienced temp

That's it! Now use the heat index value to guide water intake, work schedules, and safety protocols.

## Applying the Information

Once you know the current heat index ranges, take appropriate actions:

• 80-90°F: Fatigue possible with prolonged exposure and activity
• 90-105°F: Sunstroke, heat cramps, and exhaustion become likely
• 105-130°F: Heatstroke highly probable with continued exertion; schedule regular cool-down breaks
• >130°F: Very high risk of heat stroke and heat exhaustion after only limited time outside

## Heat Index Formula

While heat index calculators automate the process, the underlying formula combines temperature and humidity into an apparent temperature.

The heat index equation leverages a regression fit against empirical physiological studies on heat exposure impacts. The key inputs are:

• T = Air Temperature (Fahrenheit)
• RH = Relative Humidity (percentage)

The formula produces an adjusted temperature reflecting perceived heat stress.

### The Math

Without getting too technical, the general form is:

Heat Index = -42.379 + 2.04901523T + 10.14333127RH - .22475541TRH - .00683783T2 - .05481717RH2 + .00122874T2RH + .00085282TRH2 - .00000199T2RH2

Don't worry about memorizing that! Just leverage the convenient online heat index calculator sites.

## Heat Index Warning Levels

 Heat Index Range Risk Level Health Hazards & Precautions 80°F - 90°F Caution Possible fatigue with prolonged exposure and activity. Basic heat safety precautions are recommended. 90°F - 105°F Extreme Caution Sunstroke, muscle cramps, and heat exhaustion become likely. Additional rest breaks and hydration are needed. 105°F - 130°F Danger High likelihood of heat illness with extended exertion. Rigorous safety protocols should be activated and enforced. Above 130°F Extreme Danger Heatstroke is highly probable with continued exertion. Physical activity should be halted; seek temperature-controlled shelter.