Heat Index Calculator

Heat Index Calculator is a clean, fast tool for finding the heat index — the "feels like" temperature — from air temperature and relative humidity, completely offline. Type a temperature, drag the humidity slider, and read how hot the air actually feels the moment you change a value.

WHAT YOU CAN DO
• Calculate the heat index from temperature and relative humidity
• Work in Celsius or Fahrenheit, for both input and output
• See a plain-language risk level: None, Caution, Extreme caution, Danger or Extreme danger
• Read a short safety note for each risk level
• View the heat index in the other unit at a glance
• Load preset conditions — Humid summer day, Dry desert heat and more — with one tap

WHY THE HEAT INDEX
Air temperature alone does not tell you how dangerous the heat is. When humidity is high, sweat evaporates more slowly, so your body cools less efficiently and the air feels much hotter than the thermometer reads. The heat index combines both into a single "feels like" number.

LEARN AS YOU GO
A built-in Learn tab explains, in plain language, what the heat index is, how the risk levels work, and simple tips for staying safe when it is hot.

HOW IT WORKS
Calculations use the US National Weather Service (Rothfusz) heat-index regression, with the standard low-humidity and high-humidity adjustments, and the simpler Steadman formula at lower temperatures.

ACCURACY & SAFETY
Results are estimates for general and educational use and offer general guidance, not medical advice. They are not a substitute for official heat warnings or professional advice. In hot conditions, drink water, take breaks in the shade or air conditioning, and seek medical help if you feel unwell.

PRIVACY
The app collects no personal data and works fully offline — your inputs never leave your device. Ads are served by Google AdMob, which may use an advertising identifier as described in Google's policies.

Light and dark themes, a tiny download, and no clutter. Download Heat Index Calculator and know how hot it really feels.