Weather Index Calculator
Calculate wind chill, heat index or dew point from temperature and humidity or wind speed.
Assumptions used in this calculation
- Formula validity ranges: Wind chill (Environment Canada) is intended for temperatures at or below 10°C with wind above ~4.8 km/h; heat index (Rothfusz regression) is intended for temperatures above ~27°C with meaningful humidity. Results outside these ranges are extrapolated and less reliable.
- Standard measurement height: Temperature and wind speed are assumed to be measured at standard outdoor conditions (roughly 1.5 m above ground, in the shade); readings from a car dashboard or a sunny thermometer will differ.
About this calculator
The temperature on a thermometer often doesn't match how conditions actually feel or behave, wind strips heat from skin faster than still air, humidity slows sweat evaporation and makes heat feel worse, and moisture content in the air isn't something a plain thermometer measures at all. This calculator computes whichever of the three is relevant to your conditions: wind chill (Environment Canada formula, from temperature and wind speed) for cold, windy weather; heat index (Rothfusz regression, from temperature and humidity) for warm, humid weather; or dew point (Magnus formula, from temperature and humidity) as a temperature-independent moisture reading. It's useful for deciding how to dress for outdoor activity, judging frostbite or heat-stress risk, or figuring out how muggy or fog-prone conditions are likely to be. These formulas involve exponents and regression coefficients that aren't practical to compute by hand, so the calculator applies the correct meteorological formula for the index and range you select.
Worked example
-10°C at 20 km/h wind
Result: -17.9°C wind chill
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