What is the feels-like temperature?
The feels-like temperature (also called apparent temperature) describes how hot or cold the air actually feels to the human body, accounting for humidity when it's warm and wind when it's cold. This calculator follows the U.S. National Weather Service (NWS) convention and works in degrees Fahrenheit and miles per hour.
How it chooses a method
The tool applies a simple, standard decision rule: if the air temperature is at or above 80°F it uses the Heat Index (humidity matters most when it's hot); if the temperature is at or below 50°F and the wind exceeds 3 mph it uses Wind Chill (wind matters most when it's cold); otherwise the feels-like value equals the actual temperature.
The formulas explained
The Heat Index uses the Rothfusz regression, a polynomial fit of temperature (\(T\)) and relative humidity (\(R\)), with small correction terms for very dry (\(R < 13\%\)) or very humid (\(R > 85\%\)) conditions:
$$\begin{gathered} \text{HI} = -42.379 + 2.04901523\,T + 10.14333127\,R - 0.22475541\,T R \\ -\,0.00683783\,T^2 - 0.05481717\,R^2 + 0.00122874\,T^2 R \\ +\,0.00085282\,T R^2 - 0.00000199\,T^2 R^2 \\[1.4em] \text{where}\quad \left\{ \begin{aligned} T &= \text{Temperature (°F)} \\ R &= \text{Humidity (\%)} \end{aligned} \right. \end{gathered}$$The Wind Chill formula combines temperature and wind speed raised to the 0.16 power to model convective heat loss from exposed skin:
$$\begin{gathered} \text{WC} = 35.74 + 0.6215\,T - 35.75\,V^{0.16} + 0.4275\,T\,V^{0.16} \\[1.4em] \text{where}\quad \left\{ \begin{aligned} T &= \text{Temperature (°F)} \\ V &= \text{Wind Speed (mph)} \end{aligned} \right. \end{gathered}$$
Worked example
At 90°F with 70% relative humidity, the Rothfusz regression returns about \(105.9\,\text{°F}\) — noticeably hotter than the thermometer reading because high humidity slows the body's ability to cool by sweating. On a 30°F day with a 15 mph wind, the Wind Chill formula gives about \(19\,\text{°F}\), so it feels roughly 11 degrees colder than the air temperature.
FAQ
Why does humidity make it feel hotter? Sweat evaporates more slowly in humid air, reducing the body's main cooling mechanism, so the effective temperature rises.
Why is wind only used when cold? Wind strips away the thin warm layer near the skin, accelerating heat loss. This effect is the basis of wind chill and is only meaningful at low temperatures.
What if it's a mild day? Between 50°F and 80°F (or with little wind), neither effect is significant, so the feels-like temperature is reported as the actual temperature.
