Humidex: how hot it feels when the air is humid
The humidex combines heat and humidity into one number that describes how hot the weather feels. At 30 °C with a dew point of 24 °C, the humidex is 41.
Updated November 7, 2026 · Sources
How the humidex is calculated
Environment and Climate Change Canada starts from the vapour pressure of the air, worked out from the dew point. The humidex adds to the temperature a share of the vapour pressure above 10 hPa: the more water vapour, the higher the humidex.
Like wind chill, the humidex is not a temperature but an index without a unit. Environment Canada only reports it when the air reaches 20 °C and the humidex is at least 1 degree above the temperature.
Humidex chart
Read the row of the air temperature, then the column of the dew point. A dash means the dew point cannot be higher than the temperature.
| Air | 10 °C | 14 °C | 18 °C | 20 °C | 22 °C | 24 °C |
|---|---|---|---|---|---|---|
| 20 °C | 21 | 23 | 26 | 28 | — | — |
| 22 °C | 23 | 25 | 28 | 30 | 31 | — |
| 25 °C | 26 | 28 | 31 | 33 | 34 | 36 |
| 28 °C | 29 | 31 | 34 | 36 | 37 | 39 |
| 30 °C | 31 | 33 | 36 | 38 | 39 | 41 |
| 32 °C | 33 | 35 | 38 | 40 | 41 | 43 |
| 35 °C | 36 | 38 | 41 | 43 | 44 | 46 |
Degrees of comfort
Environment Canada groups humidex values into four degrees of comfort:
- Little discomfort: 20 … 29.
- Some discomfort: 30 … 39.
- Great discomfort, avoid exertion: 40 … 45.
- Dangerous, possible heat stroke: 46 and above.
Humidex or heat index?
The humidex is Canadian and uses the dew point; the American heat index uses relative humidity and its own scale in °F. The two numbers are not interchangeable.