Heat Index Calculator
Calculate the heat index (feels-like temperature) using air temperature and relative humidity or dew point.
Heat Index Calculator: Estimate the Real Feel Temperature
The Heat Index Calculator helps you determine the “feels-like” temperature based on air temperature and relative humidity. This tool is essential for understanding how weather conditions impact the human body, especially during hot and humid days.
How to Use the Heat Index Calculator
Option 1: Using Relative Humidity
- Enter the air temperature in Fahrenheit (°F), Celsius (°C), or Kelvin.
- Input the relative humidity percentage.
Option 2: Using Dew Point Temperature
- Enter the air temperature in Fahrenheit (°F), Celsius (°C), or Kelvin.
- Input the dew point temperature in the same units.
What is the Heat Index?
The heat index, sometimes called “humiture,” measures the perceived temperature rather than the actual air temperature. For example, if the air temperature is 83°F with a relative humidity of 70%, the feels-like temperature would be 88°F. This is because high humidity reduces the body’s ability to cool itself through sweat evaporation, making it feel hotter than it actually is.
Heat index is similar to the wind chill index, which calculates perceived cold temperatures. However, the heat index is primarily used for outdoor conditions during hot weather. Factors like hydration, body shape, metabolism, and activities can also influence how heat is perceived.
Why is the Heat Index Important?
Understanding the heat index is crucial for preventing heat-related illnesses. High heat index values can lead to overheating, dehydration, and even more serious conditions like heat exhaustion or heat stroke. Exposure to direct sunlight can also increase the heat index by up to 14°F, making it even more important to stay informed about weather conditions.
Effects of the Heat Index: Know the Risks
The chart below outlines the potential risks associated with heat index values:
| Heat Index (°F) | Risk Level | Effects |
|---|---|---|
| 80-90°F | Caution | Possible fatigue with prolonged exposure and activity. Heat cramps may occur. |
| 90-105°F | Extreme Caution | Heat cramps and exhaustion are possible. Sustained activity may result in heat stroke. |
| 105-130°F | Danger | Heat cramps and exhaustion are likely. Heat stroke is probable with continued exposure. |
| Over 130°F | Extreme Danger | Heat stroke is imminent. |
How is the Heat Index Calculated?
The National Weather Service (NWS) developed the heat index formula based on factors like air temperature, relative humidity, and wind speed. This calculation applies to temperatures of 80°F or higher and relative humidity levels of 40% or more.
While the formula provides a general guideline, individual factors such as clothing, activity level, and hydration can impact how accurate the heat index feels.
Stay Safe in High Heat Index Conditions
High heat index values present real health risks, especially for vulnerable groups such as:
- Children: Larger skin surface, higher heat production, and less sweating increase their risk of overheating.
- People with health conditions: Obesity, diabetes, heart disease, and other conditions can limit the body’s ability to cool down.
- Outdoor workers and athletes: Heavy physical exertion increases the risk of dehydration and heat-related illnesses.
Pro Tip: Thirst is a late sign of dehydration. Stay hydrated by drinking water before, during, and after activities, especially in high heat and humidity.
Related Tools
- Wind Chill Calculator – Estimate perceived cold temperatures.
- Dew Point Calculator – Measure moisture levels in the air.
By understanding the heat index and its effects, you can better prepare for hot weather, stay safe, and avoid heat-related illnesses. Use our Heat Index Calculator to plan outdoor activities and protect yourself from extreme heat conditions.