Heat Index Calculator
Work out how hot it really feels from air temperature and relative humidity using the NWS Rothfusz heat index formula, with caution and danger bands.
אודות Heat Index Calculator
The Heat Index Calculator converts an air temperature and a relative humidity reading into the apparent temperature — how hot it actually feels to the human body. Humid air slows the evaporation of sweat, which is how you shed heat, so a 32 °C day at 70% humidity feels far hotter than the same temperature in dry air.
The tool implements the US National Weather Service Rothfusz regression, including the low-humidity and high-humidity adjustments that the NWS applies at the edges of its range, and falls back to the simpler Steadman average below 27 °C (80 °F) exactly as the official method does.
Use it to decide whether outdoor work, sport or training should be moved, shortened or shaded, and to know which NWS caution band the day falls into. Free, instant and computed in your browser.
כיצד להשתמש ב-Heat Index Calculator
- Choose whether you are entering temperatures in °C or °F.
- Enter the current air temperature.
- Enter the relative humidity as a percentage.
- Read the heat index — the apparent temperature — and how much hotter it feels.
- Check the caution band before planning outdoor activity.