Heat Index & Wind Chill Calculator
Find the 'feels like' temperature: heat index from temperature and humidity, or wind chill from temperature and wind speed, using the US National Weather Service formulas.
How to use
- 1Choose heat index or wind chill and your units.
- 2Enter the air temperature and humidity (or wind speed).
How it's calculated
Heat index: NWS Rothfusz regression (with adjustments) for 80 °F and above. Wind chill (NWS 2001): 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16, valid at or below 50 °F with wind over 3 mph.
Frequently asked questions
When is heat index dangerous?
NWS categories: 80–90 °F caution, 90–103 °F extreme caution, 103–124 °F danger, 125 °F+ extreme danger — heat illness becomes likely.
When does frostbite become a risk?
At wind chills around −18 °F (−28 °C), exposed skin can freeze in about 30 minutes; colder values shorten that a lot.
Is heat index measured in shade?
Yes — direct sunshine can add up to about 15 °F (8 °C) to the heat index.