Heat Index Calculator

Calculate how hot it actually feels outside by combining air temperature and humidity levels. The heat index, also known as the “feels like” temperature or humiture, helps you understand the perceived temperature your body experiences.

What is Heat Index?

Heat index is a measurement that combines air temperature and relative humidity to determine how hot it actually feels to the human body. For example, an air temperature of 83°F with 70% relative humidity would feel like 88°F to your body. This difference occurs because high humidity reduces your body’s ability to cool itself through sweating.

How to Use This Calculator

1. Enter the air temperature in your preferred unit (Fahrenheit, Celsius, or Kelvin)
2. Input either:
   • Relative humidity percentage (most common)
   • OR Dew point temperature (for more precise calculations)
3. The calculator will show you the “feels like” temperature and any associated health risks

Understanding the Results

The heat index value indicates potential health risks:

Heat Index Range	Risk Level	Health Concerns
80-90°F (27-32°C)	Caution	Fatigue possible with prolonged exposure
90-105°F (32-41°C)	Extreme Caution	Heat cramps and exhaustion possible
105-130°F (41-54°C)	Danger	Heat cramps/exhaustion likely, heat stroke probable
Over 130°F (54°C)	Extreme Danger	Heat stroke imminent

Important Safety Notes

• Full sun exposure can increase heat index values by up to 14°F
• Children are at greater risk due to:
  • Larger skin surface relative to body size
  • Higher heat production during exercise
  • Less sweating than adults
  • Lower awareness of hydration needs
• High-risk individuals include those with:
  • Obesity
  • Diabetes
  • Heart disease
  • Cystic fibrosis
  • Mental health conditions

Tips for High Heat Index Days

1. Stay hydrated before feeling thirsty
2. Limit outdoor activities during peak heat
3. Wear light, loose-fitting clothing
4. Take frequent breaks in air-conditioned spaces
5. Check on vulnerable individuals
6. Never leave children or pets in parked vehicles

Technical Notes

• This calculator uses the National Weather Service (NWS) heat index equation
• Most accurate for:
  • Temperatures of 80°F (27°C) or higher
  • Relative humidity of 40% or more
  • Shaded locations with light wind conditions
• Values may vary based on individual factors like:
  • Body mass and height
  • Clothing
  • Physical activity level
  • Wind speed