Enter the current temperature and relative humidity into the calculator to determine the heat index.

Heat Index Formula

The following formula is used to calculate a heat index.

HI = .5 * [ T + 61.0 + [(T-68)*.12] + (RH*.094)]

Temperature (F) measures the average kinetic energy of the particles in a substance on the Fahrenheit scale.

Relative humidity refers to the amount of moisture in the air compared to the maximum amount it can hold at a given temperature, expressed as a percentage.

Heat Index Definition

Heat Index is a measure that combines air temperature and relative humidity to determine how hot it feels to the human body. It is important because it helps us understand the potential risk of heat-related illnesses such as heat stroke and heat exhaustion.

By considering both temperature and humidity, the Heat Index provides a more accurate representation of the actual discomfort caused by heat.

This information is crucial for individuals who work or engage in outdoor activities, as it helps them take appropriate precautions to prevent heat-related health problems.

Heat Index Example

How to calculate heat index?

  1. First, determine the relative humidity.

    Using the calculator linked above, determine the relative humidity.

  2. Next, determine the current temperature.

    Measure the temperature using an accurate thermometer.

  3. Finally, calculate the heat index.

    Using the HI formula, determine the heat index using the information from steps 1 and 2.


Why is the heat index important for health and safety?

The heat index is crucial for health and safety because it helps individuals understand the risk of heat-related illnesses, such as heat stroke and heat exhaustion, especially during hot and humid weather. It guides people in taking necessary precautions to stay safe.

How can I protect myself from heat-related illnesses?

To protect yourself from heat-related illnesses, stay hydrated, wear lightweight and light-colored clothing, take frequent breaks in shaded or air-conditioned areas, and avoid strenuous activities during the hottest parts of the day.

Can the heat index be used for any temperature and humidity level?

The heat index is most relevant and accurate at higher temperatures and humidity levels. It may not provide meaningful information in very dry conditions or when the temperature is cool.

How is relative humidity calculated?

Relative humidity is calculated by comparing the current amount of moisture in the air to the maximum amount of moisture the air can hold at a given temperature. This is often done using hygrometers or through calculations based on dew point and temperature readings.

heat index calculator
heat index formula