What Does Feels Like Temperature Mean?

The short answer

The "feels like" temperature estimates how the air will affect your body once humidity or wind gets factored in. On hot days, weather services use the heat index, which adds the effect of humidity. On cold, windy days, they use wind chill, which adds the effect of wind on bare skin. Meteorologists call the general idea "apparent temperature" (Rothfusz 1990).

What "feels like" actually measures

Your body runs at about 98.6°F (37°C) and constantly sheds heat to the air around it. How fast it sheds heat depends on more than the thermometer reading. Humid air slows sweat evaporation, so you hold onto heat. Wind strips heat off your skin, so you lose it faster.

The feels like number translates that heat exchange back into a single temperature. When your app says "92°F, feels like 105°F," it means the air and humidity together load your body about as much as 105°F air would under the model's reference conditions.

That last phrase matters. Every feels like formula assumes a specific person in a specific situation. We'll get to who that person is in a minute.

How the heat index works

The National Weather Service (NWS) defines the heat index as "a measure of how hot it really feels when relative humidity is factored in with the actual air temperature" (NWS Heat Index).

The science goes back to Robert Steadman's 1979 work on "sultriness," which modeled heat flow between skin, clothing and air. In 1990, NWS meteorologist Lans Rothfusz fit a regression equation to Steadman's tables, and forecasters still use a version of it today. The equation carries an error of about ±1.3°F (Rothfusz 1990).

Humidity drives the whole thing. Sweat cools you only when it evaporates. In muggy air, evaporation slows, sweat drips off instead of cooling you, and your core temperature climbs.

A small heat index chart

These values come from the NWS heat index equation, rounded to the nearest degree. The two 100°F rows with 15% and 55% humidity match examples the NWS publishes.

| Air temperature | Relative humidity | Heat index (feels like) | |---|---|---| | 90°F (32°C) | 40% | 91°F (33°C) | | 90°F (32°C) | 60% | 100°F (38°C) | | 90°F (32°C) | 80% | 113°F (45°C) | | 100°F (38°C) | 15% | 96°F (36°C) | | 100°F (38°C) | 40% | 109°F (43°C) | | 100°F (38°C) | 55% | 124°F (51°C) |

Notice the 15% row. In very dry air, the heat index can come out below the air temperature, because sweat evaporates so well.

The shade problem

Heat index assumes you stand in the shade. The NWS says "exposure to full sunshine can increase heat index values by up to 15°F" (NWS Heat Index). So a 100°F heat index at a shady bus stop could feel closer to 115°F (46°C) on an open parking lot.

How wind chill works

Wind chill handles the cold side. The NWS replaced its old index with a new Wind Chill Temperature index on November 1, 2001. The new version models heat loss from a human face, estimates wind at face height (about five feet), and assumes no help from the sun (NWS 2001).

The NWS defines wind chill only at air temperatures at or below 50°F (10°C) and wind speeds above 3 mph. Its example: at 0°F (minus 18°C) with a 15 mph wind, the wind chill reaches minus 19°F (minus 28°C) (NWS Wind Chill).

Above 50°F, wind chill drops out, and most forecasts switch to heat index once it gets hot and humid. In the mild middle, many apps simply show a feels like value close to the air temperature.

How weather apps calculate "feels like"

Each app picks its own recipe, and most don't publish the exact formula. Here's what we can verify:

• Apple Weather and WeatherKit: Apple's developer documentation describes apparentTemperature as "the feels-like temperature when factoring wind and humidity" (Apple WeatherKit). Apple doesn't publish the formula.
• National Weather Service: uses heat index in warm weather and wind chill in cold weather, with the formulas and limits above (NWS Heat Index; NWS Wind Chill).

So when two apps disagree by a few degrees, they're often using different models or different weather data for your spot. Neither one is broken.

Feels like vs actual temperature: which is more accurate?

They answer different questions. The actual temperature tells you how warm the air is. The feels like number estimates how that air treats a human body. For deciding what to wear, how hard to exercise, or whether heat could make someone sick, feels like usually tells you more.

Still, the "someone" in the formula matters. Steadman's heat index model assumes an adult about 5 feet 7 inches tall and 147 pounds, wearing long trousers and a short-sleeved shirt, walking at about 3.1 mph in a light breeze of about 5 knots (Rothfusz 1990). If that isn't you right now, your real experience can differ.

What the feels like number leaves out

The standard formulas use air temperature, humidity and wind. Plenty of things change how warm you feel without changing any of those:

• Sun on your skin. Direct sun can add up to 15°F to the heat index (NWS Heat Index), and wind chill assumes no sun at all (NWS 2001).
• A parked car's solar load. Sun through glass heats a closed cabin far beyond the outdoor air (more on this below).
• Your clothing. The model assumes trousers and a short-sleeved shirt (Rothfusz 1990). A suit, a puffy jacket or a tank top changes the picture.
• What you're doing. The model person walks at a steady pace. Running, mowing or sitting still shifts how much heat your body makes.
• Body size. The model uses one adult body (about 5 feet 7 inches and 147 pounds), so a small child or a much larger adult falls outside its assumptions.
• Acclimatization. Someone who has spent a couple of weeks in the heat handles it better than someone who just flew in from Minneapolis.
• Indoor radiant heat. Indoors, warm walls, sunny windows and cold glass all radiate heat to or from you. An outdoor feels like number can't see any of that.

If you've ever wondered why one person in the room runs warm and another reaches for a sweater, these factors explain a lot of it. Our guides on why you might always feel hot and why the perfect temperature changes dig into the personal side.

Feels like temperature in a car cabin

A closed car on a sunny day builds its own weather. In a Stanford study, researchers measured a dark sedan on 16 clear days with outdoor temperatures of 72 to 96°F (22 to 36°C). The cabin warmed by an average of 3.2°F every 5 minutes, about 80% of the rise came in the first 30 minutes, and the interior climbed roughly 40°F (22°C) above the outside air within an hour. Even on the coolest day, the cabin hit 117°F (47°C). Cracking the windows 1.5 inches didn't meaningfully slow the rise (McLaren 2005).

That means the outdoor feels like number on your phone tells you very little about what you'll sit down into. Seat surfaces, the steering wheel and the dashboard all soak up sun and radiate it back. Just Right adjusts your Tesla cabin for weather, sun and time of day for this reason. For the vehicle side, see our guide to Tesla Cabin Overheat Protection.

And please, never leave a child or pet in a parked car, even for a quick errand. If you see one inside a hot car, call 911. Our guide to heat stress symptoms covers the warning signs.

The bottom line

The feels like temperature folds humidity (heat index) or wind (wind chill) into the air temperature to estimate what your body experiences. Use it over the raw temperature when you decide what to wear or how hard to push outside. Then adjust for what the formula can't see: direct sun, a hot car, your clothes, your activity and how used to the heat you are. Know your numbers, and know which number you're looking at.