The heat index, sometimes called the apparent temperature, combines air temperature and relative humidity to estimate how hot it actually feels to the human body. When humidity is high, sweat evaporates slowly, so your body cannot cool itself as efficiently and the effective temperature climbs well above the reading on the thermometer. This calculator uses the same Rothfusz regression that the United States National Weather Service publishes, including the low humidity and high humidity adjustments, so the numbers match official heat advisories. Enter the air temperature and the relative humidity, choose Fahrenheit or Celsius, and read the heat index along with a caution level. It is useful for planning outdoor work, exercise and events during summer heat waves. Everything is computed locally in your browser for instant, private results.
The heat index, sometimes called the apparent temperature, combines air temperature and relative humidity to estimate how hot it actually feels to the human body. When humidity is high, sweat evaporates slowly, so your body cannot cool itself as efficiently and the effective temperature climbs well above the reading on the thermometer.
Yes. Heat Index Calculator is completely free, with no sign-up and no usage limits.
Yes. Heat Index Calculator runs in any modern web browser. There is nothing to download or install.
Yes. Heat Index Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.