Wind Chill & Heat Index Calculator

Calculate how the weather actually feels, not just what the thermometer says. Wind chill accounts for how wind accelerates heat loss from skin in cold weather; heat index accounts for how humidity impairs sweat evaporation in hot weather. Both use the official US National Weather Service formulas.

°F
mph
Feels like
19 °F
Note

How it works

Wind chill combines air temperature and wind speed using an empirical formula developed from skin heat-loss experiments. Heat index combines air temperature and relative humidity using a regression formula fitted to Steadman's original heat-stress research. Both are only defined (and reliable) within specific ranges: wind chill for 50°F and below with wind above 3 mph, heat index for roughly 80°F and above.

Formula
Wind chill = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16) | Heat index = Rothfusz regression on T and RH (NWS/NOAA)

Example. 30°F with a 15 mph wind feels like about 19°F. 95°F at 60% humidity feels like roughly 113°F.

Frequently asked questions

Why does wind make cold feel so much worse?

Wind strips away the thin layer of warmed air that naturally forms next to your skin, forcing your body to keep re-heating a constantly replaced layer of cold air - which pulls heat away much faster than still air at the same temperature.

Why does humidity make heat feel worse?

Your body cools itself mainly by evaporating sweat. High humidity means the air is already close to saturated with moisture, so sweat evaporates more slowly and cools you less effectively, even though the air temperature itself hasn't changed.

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