Calculate the apparent temperature — wind chill for cold weather, heat index for hot and humid conditions.
The apparent temperature is what your body feels, not what the thermometer reads. In cold and windy conditions, wind strips heat from exposed skin faster than still air does — the wind chill formula (Environment Canada) quantifies this for temperatures below 10 °C and winds above 4.8 km/h.
In hot and humid conditions, sweat evaporates more slowly, and the body cannot cool itself as efficiently. The heat index (Rothfusz, NWS) combines temperature and relative humidity to express the perceived heat. Above 40 °C heat index, heat exhaustion becomes a real risk.
This calculator applies the wind chill formula when the temperature is below 10 °C and wind is given, and the heat index when the temperature is above 27 °C and humidity is given. In between, the apparent temperature is close to the actual one.
Wind chill: 13.12 + 0.6215T − 11.37V^0.16 + 0.3965TV^0.16 (T in °C, V in km/h). Heat index: Rothfusz regression (NWS).
Because wind accelerates heat loss from exposed skin. The colder and windier it is, the faster your skin temperature drops.
Slightly, but the wind chill formula does not include humidity. Wind is the dominant factor in cold weather.
Above 40 °C is caution, above 54 °C is extreme danger. Prolonged exposure above 40 °C risks heat exhaustion.
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