Heat Index Calculator: get an approximate value for the heat index, based on the current temperature in Farenheit, and the relative humidity.

Heat Index Calculator

Select your units, and then enter the temperature and relative humidity. Click 'Calculate!' to find the heat index.



Relative humidity

About the Calculator

"It's not the heat, it's the humidity!" That's what people say when the weather is hot and "sticky." Living in Maine, I find temperatures above 80 unbearable, but it's because of the humidity in the air; when I spent a week in Beersheba, Israel, we saw temperatures as high as 114, and it was more tolerable, because the air was so dry.

So what is the heat index? The heat index is a way of describing what the temperature "feels" like (similar to Wind Chill). There are a variety of websites which have formulas to do this calculation. Surprisingly, most of those sites have the same incorrect formula, which is identical to the incorrect formula posted on the National Weather Service website. Amusingly, their own formula doesn't match the table of values they have posted!

This formula has been partially verified against the table of values on the NWS website.