Heat Index Calculator (Feels Like Temp)

🌡️ Heat Index Calculator feels like

The Heat Index estimates how hot it really feels when humidity is added to air temperature. High humidity reduces sweat evaporation, making it feel hotter than the actual temperature.

🌡️ Air Temperature

°F: 70–120 | °C: 21.1–48.9

📏 Unit

💧 Relative Humidity (%)

Range: 0 – 100%

📌 What is Heat Index & why humidity matters

Heat index, commonly known as the “feels like” temperature, combines air temperature and relative humidity to reflect how the human body perceives warmth. When humidity is high, sweat evaporates slowly, reducing the body's natural cooling. The National Oceanic and Atmospheric Administration (NOAA) developed the complex formula used here.

At lower humidity, sweat evaporates quickly, sometimes making it feel cooler than the actual air temperature. But as humidity rises above 40–50%, the heat index can exceed the real temperature by 10°F or more. Prolonged exposure to a heat index above 90°F (Extreme Caution) may lead to heat cramps or exhaustion. Above 103°F (Danger) heat cramps or heat exhaustion are likely, and at 125°F+ (Extreme Danger) heat stroke is highly possible. Always stay hydrated and limit outdoor activity during high heat index values.

Use this calculator: Enter a temperature (70–120°F or equivalent 21–49°C) and relative humidity (0–100%) to get the current heat index and its safety category.