Estimate apparent temperature using air temperature and relative humidity. This free weather calculator helps users understand how hot conditions may actually feel.
Enter temperature in Fahrenheit and relative humidity to estimate heat index.
This calculator uses the standard warm-weather heat index approximation commonly used in U.S. weather products.
Heat index is the apparent temperature felt by the human body when air temperature and humidity are combined. When humidity is high, sweat evaporates less efficiently, making hot weather feel even hotter.
Heat index is often used for weather awareness, outdoor planning, training conditions, and heat safety.
No. Heat index is the temperature the body may feel like it is experiencing when humidity is included.
Heat index is most useful in warm, humid conditions. In cooler or very dry conditions, it is less meaningful.
High humidity slows the evaporation of sweat, reducing the body’s ability to cool itself.
Yes. Heat stress and environmental conditions can affect comfort, workload, and outdoor performance during hot weather.