Humidex Calculator
Canadian humidex and comfort from temps.
What it does
Humidex translates muggy into misery numbers: 30 C air with 20 C dewpoint feels 38 to Canadian forecasts. Dewpoint drives the index harder than heat.
The tool above takes air temp with dewpoint in Celsius. It returns humidex with the comfort band and advice.
The default 30 and 20 gives 38 for some discomfort. The 35 and 25 case gives 47, dangerous, and 25 with 15 gives 29, comfortable.
Environment services publish the vapor pressure equation behind the index with matching comfort bands. Weather programs repeat the readings for public heat guidance.
Bands guide behavior, not diagnosis: shade, water, and rest answer high readings. Indoor humidex differs while night resets exposure.
How to use
- Type air temp in C.
- Type dewpoint in C.
- Read humidex first.
- Read comfort beside it.
- Read advice last.
- Hydrate past 40.
Formula
- T
- Air temperature in Celsius.
- D
- Dewpoint in Celsius.
Environment Canada publishes the humidex equation with dewpoint vapor math matching this engine. Weather service programs mirror the same comfort bands for public guidance. Dewpoint above air temp is unphysical, so the tool refuses it.
Worked example
Example: muggy 30 degrees
Defaults: 30 C air, 20 C dewpoint.
- Day: 30 C air with 20 C dewpoint.
- Vapor: 6.11 x e^(5417.753 x (1/273.16 minus 1/293.15)).
- Humidex: 30 + 0.5555 x (23.65 minus 10) = 38.
- Band: 30 to 39 reads some discomfort.
- Advice: typical summer day, hydrate normally.
- Tool shows 38, Some discomfort, Typical summer day.
Reference table
| Humidex | Comfort | Action |
|---|---|---|
| Under 30 | Comfortable | Normal day |
| 30 to 39 | Some discomfort | Hydrate |
| 40 to 45 | Great discomfort | Shade and water |
| Over 45 | Dangerous | Avoid exertion |
Limits
- Celsius inputs only.
- Outdoor shade assumed.
- Bands guide, not diagnose.
- Wind unread here.
Common mistakes
- Reading humidex as temp.
- Dewpoint past air temp.
- Ignoring shade differences.
- Skipping water breaks.
- Trusting indoor readings.
Try it yourself
Quick checks. Answers sit tucked under each question.
35 C with dewpoint 25?
47 with dangerous comfort: drink water, seek shade.
25 C with dewpoint 15?
29 with comfortable air: typical summer day.
Dewpoint 35, air 30?
Dewpoint cannot exceed air temp: check the inputs.
Questions
Humidex meaning?
Air temp plus humidity math from dewpoint. Higher dewpoints lift it faster than heat alone.
Comfort bands?
Under 30 comfortable, 30-39 some discomfort, 40-45 great discomfort, over 45 dangerous.
Heat index same?
Yes, different formulas, close readings. Humidex runs Canadian forecasts.
Dewpoint above temp?
No, dewpoint cannot pass air temp. The tool refuses such skies.
Real feel exact?
Yes, shade, wind, and night reset exposure. Indoor readings differ.
Medical advice?
No, this screens comfort. Heat illness needs shade, water, and care, never arithmetic.