🥵 Humidex Calculator
Enter the air temperature and dew point to get the humidex and how it feels.
Humidex
42°C
Great discomfort; avoid exertion
Humidex is Environment Canada\'s "feels-like" index for humid heat: humidex = T + 0.5555 × (e − 10), where e is the vapour pressure from the dew point. It\'s unitless but read on the same scale as temperature. Guidance: under 30 comfortable, 30–39 some discomfort, 40–45 great discomfort, 46+ dangerous. Unlike the US heat index it uses dew point rather than relative humidity. 🔒 In your browser.
How the humidex calculator works
Humidex is the index Environment Canada uses to describe how hot humid air actually feels. It combines the air temperature with the moisture in the air (from the dew point): humidex = T + 0.5555 × (e − 10), where e is the water-vapour pressure derived from the dew point. Higher dew points mean more humidity and a higher humidex. It's reported without units but read on the same scale as temperature — a humidex of 40 feels like oppressive heat even if the thermometer says 31.
Humidex uses the dew point, whereas the US heat index uses relative humidity — they measure the same discomfort differently and give slightly different numbers. Environment Canada's comfort guide: below 30 is comfortable, 30–39 causes some discomfort, 40–45 great discomfort (avoid exertion), and 46 or above is dangerous with heat-stroke risk.
Frequently asked questions
What is humidex?
Humidex is Environment Canada's measure of how hot it feels when humidity is factored in, combining air temperature and dew point into a single number read on the temperature scale. A humidex of 40+ means it feels oppressively hot.
How is humidex calculated?
humidex = T + 0.5555 × (e − 10), where T is the air temperature in °C and e is the vapour pressure (in hPa) computed from the dew point: e = 6.11 × exp(5417.7530 × (1/273.16 − 1/dewpoint_K)).
What is the difference between humidex and heat index?
Both describe how hot humid air feels, but humidex (Canada) uses the dew point while the US heat index uses relative humidity. They're calculated differently and can give slightly different values for the same conditions.
What humidex is dangerous?
Environment Canada considers 40–45 to cause great discomfort (avoid exertion) and 46 or higher to be dangerous, with heat stroke possible. Below 30 is generally comfortable and 30–39 causes some discomfort.
Why does humidex use dew point instead of humidity?
Dew point is a direct measure of the actual moisture in the air, independent of temperature, so it maps cleanly to vapour pressure. That makes the humidex formula straightforward — though you can convert relative humidity and temperature to a dew point first.