How "Feels Like" Temperature Is Calculated

“Feels like” temperature (also called apparent temperature) is an attempt to translate weather conditions into how warm or cold they tends to feel on exposed skin. It is not a direct measurement from a thermometer: it’s a calculated value that usually combines air temperature with humidity and/or wind.

In most forecasts and weather apps, “feels like” is computed using one of two different indices depending on conditions:

1) When it’s cold: wind chill

Wind speeds up heat loss from your skin by disrupting the thin insulating layer of warmer air near your body. That’s why a windy 0°C can feel colder than a calm 0°C.

One widely used formula is the NWS/Environment Canada wind chill index (air temperature in °C, wind speed at 10 m in km/h):

WCI = 13.12 + 0.6215T - 11.37V^0.16 + 0.3965TV^0.16

Where:

• T is air temperature in °C
• V is wind speed in km/h

Notes:

• Wind chill is meant for cool/cold air temperatures and meaningful wind (not calm conditions).
• Different services use slightly different thresholds for when to apply it.

2) When it’s hot: heat index (temperature + humidity)

When humidity is high, sweat evaporates more slowly. Evaporation is one of your body’s main cooling mechanisms, so reduced evaporation makes hot air feel hotter.

In the US, many products use the NWS heat index, commonly based on the Rothfusz regression (temperature and relative humidity). Other countries may show Humidex (Canada) or other apparent-temperature formulas, but the idea is the same: combine heat with moisture to approximate human discomfort.

Notes:

• Heat-index style formulas are typically applied only above a warm threshold (often around 27°C / 80°F).
• In very dry air, “feels like” can be lower than the air temperature because sweat evaporates efficiently.

Why different sources don’t always match

“Feels like” is not one universal number. Two apps can show different values because they may:

• Use different indices (heat index vs humidex vs apparent temperature).
• Assume different wind averaging (gust vs sustained, height above ground, station exposure).
• Include or ignore sun/heat radiation and cloud cover.
• Use different rounding and threshold rules (“use wind chill below X”, “use heat index above Y”).

What “feels like” does not include

Even when computed correctly, it usually does not fully capture:

• Clothing and activity level (running vs standing still).
• Sun angle and direct solar radiation (sunny winter days can feel warmer than the wind chill suggests).
• Shade vs sun, wet skin, and local sheltering from wind.

A practical takeaway

Treat “feels like” as a quick risk/comfort indicator, not as a replacement for the real air temperature:

• For cold exposure risk, check wind + air temperature (wind chill conditions).
• For heat stress risk, check humidity + temperature (heat index / humidex conditions), and consider sun exposure.