Humidex Calculator (Canadian Heat and Humidity Index)

What this tool does

The humidex is the number Canadian forecasts use to describe muggy heat: it adds to the air temperature the extra warmth that the water vapour in the air makes you feel. A day of 30 °C with a 20 °C dew point feels like 38, one with a 24 °C dew point like 41. Environment Canada reads values of 30 to 39 as some discomfort, 40 to 45 as great discomfort in which exertion should be avoided, and above 45 as dangerous. The dew point, not the relative humidity, is what matters, which is why the tool asks for it.

Formula

Humidex = T + 0.5555 (e − 10) · e = 6.11 exp[5417.7530 (1 ÷ 273.16 − 1 ÷ (T_d + 273.15))] hPa

Variables

Worked example

Limitations

• The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
• The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.