About this tool
The Humidex Calculator computes the Canadian humidex, an index that expresses how hot the air actually feels once humidity is taken into account. Developed by Environment Canada, it combines the air temperature with the moisture content (via the dew point) into a single 'feels-like' temperature in degrees Celsius, and it is the headline discomfort number in Canadian summer forecasts.
The formula is Humidex = T + 0.5555·(e − 10), where T is the air temperature in °C and e is the vapor pressure computed from the dew point: e = 6.11 · exp( 5417.7530 · (1/273.16 − 1/(273.15 + Td)) ) in hPa, with Td the dew point in °C. Because it is anchored to vapor pressure and dew point rather than a temperature–humidity regression, humidex differs from the US Heat Index and is not directly comparable to it.
Everything runs in your browser. Enter the air temperature and dew point (°C or °F); the calculator returns the humidex in °C and °F plus the comfort band: below 20 no discomfort, 20–29 comfortable, 30–39 some discomfort, 40–45 great discomfort (avoid exertion), and 46 or above dangerous with heat stroke likely. Since a dew point cannot exceed the air temperature, such input is rejected.