Heat Index Explained: Why It Feels Hotter Than the Thermometer Says

You have probably seen a weather app show a 'feels like' figure higher than the temperature. One common way of estimating this is the heat index.

Temperature vs heat index

Air temperature is measured by a thermometer in the shade. The heat index combines temperature with relative humidity to estimate how hot conditions feel to the human body.

Why humidity matters

The body cools itself mainly through sweat evaporating. When the air already holds a lot of moisture, evaporation slows, so the same temperature feels hotter.

How it is calculated

A widely used formula was developed by the US National Weather Service. It is designed for shaded conditions with light wind. Direct sun can make conditions feel hotter still.

Using it sensibly

The heat index is an estimate, not a medical measurement. Use it to plan your day, and follow official advisories from local authorities during heatwaves.

See live temperature and heat index for your city on our city pages.