Just RightThe short answer
The "feels like" number on a US weather app comes from one of two National Weather Service formulas. At 80°F and up, the heat index adds the effect of humidity; at 50°F and below with wind over 3 mph, wind chill adds the effect of wind. In between, it feels like the air temperature. The heat index assumes shade and light wind, and full sun can push it up by as much as 15°F (NWS heat index).
How it works
For warm air the calculator runs the Weather Prediction Center's procedure: a simple formula first, then the Rothfusz regression with its low and high humidity adjustments once the result reaches 80°F (NWS WPC). For cold, windy air it uses the 2001 NWS wind chill formula (NWS wind chill). The dew point comes from the NWS vapor pressure formula, solved backward from your temperature and humidity (NWS vapor pressure).
The car and thermostat numbers use Just Right's default starting rule before it learns anything about you: start at 72°F in the car and 70°F at home, cool a little when it feels hot out, warm a little when it feels cold, then add 2°F if you run cold or take off 2°F if you run hot. In heat and sun, the car setting stays high enough for the fan to run quietly. Tesla accepts settings from 60 to 82°F.
Common questions
How is feels like temperature calculated?
In the US, weather apps use the National Weather Service heat index when it's 80°F or warmer and the wind chill when it's 50°F or colder with wind over 3 mph. Otherwise the feels like temperature equals the air temperature.
Does the heat index include sun?
No. The National Weather Service built the heat index for shade and light wind, and says full sunshine can raise heat index values by up to 15°F.
What's the difference between dew point and humidity?
Relative humidity tells you how close the air is to saturated at its current temperature, so it swings through the day. Dew point measures the actual moisture in the air, so a higher dew point means muggier air at any temperature.
This tool shares general information and does not give medical advice. It cannot diagnose or treat any condition. For symptoms that worry you, see a clinician. In an emergency, call 911.