What Is Humidex? Canada’s “Feels Like” Temperature—Now on the Kestrel 5400

April 24, 2026 Jackie Fitzpatrick Comments

When people say, "It feels hotter than the temperature,” they're describing something real.

Humidex is widely used in Canada as a "feels like” temperature-but it's not a heat stress standard like WBGT.

Instead, it's a regional metric used in Canadian weather reporting and workplace guidance to describe how heat and humidity combine to impact perceived temperature. And now, it's available directly on the Kestrel 5400 Heat Stress Tracker.

What Is Humidex?

Humidex (short for humidity index) is a metric developed in Canada to describe how hot the weather actually feels by combining air temperature and moisture in the air.

Unlike raw temperature, Humidex reflects perceived heat because humidity directly affects your ability to cool yourself.

High humidity = sweat doesn't evaporate
Less evaporation = less cooling
Result = it feels hotter than the thermometer shows

That's why a 90°F day can feel like 105°F when humidity is high.

Why Humidex Is Used

Humidex is commonly referenced in Canadian forecasts and workplace guidance as a way to communicate how conditions may feel to individuals.

It provides a simple, standardized number that helps:

Translate temperature and humidity into a single value
Communicate discomfort levels clearly
Align with regional expectations in Canada

Humidex Risk Levels

Humidex	What It Means
20-29	Little to no discomfort
30-39	Noticeable discomfort
40-45	High discomfort-avoid exertion
45+	Dangerous-heat stroke possible
54+	Heat stroke imminent

Important: These ranges describe comfort levels, not regulated heat stress thresholds.

How Humidex Is Calculated

At its core, Humidex combines:

Air temperature
Moisture in the air (via dew point)

The standard formula is:

H = T_air+0.5555(e-10)

Where e represents vapor pressure derived from the dew point.

Key takeaway:

Humidex is designed to reflect perceived heat, not total environmental heat stress.Humidex vs. WBGT (Understanding Their Roles)

While Humidex is useful in certain contexts, it serves a different purpose than WBGT.

Humidex is used for:

Canadian weather reporting
Public-facing communication
Describing perceived heat

WBGT is used for:

Occupational heat safety
Athletic guidelines
Environmental heat stress assessment

WBGT accounts for additional critical factors like:

Solar radiation
Wind speed
Radiant heat from surroundings

Humidex does not include these variables.

This means it should not be used as a standalone metric for heat safety decisions.

Why Humidex on the Kestrel 5400 Matters

Humidex is widely used in Canada as part of workplace guidance and public weather reporting. For organizations operating under Canadian policies, it's a familiar and often expected reference point.

Adding Humidex to the Kestrel 5400 Heat Stress Tracker makes it easier to:

Align with Canadian guidelines

Reference Humidex where it's required or commonly used

Standardize communication

Use the same metric teams, regulators, and forecasts are already referencing

Work more efficiently in the field

Access Humidex directly on-device without needing to calculate or cross-reference

This update ensures the Kestrel 5400 supports both global heat stress best practices with WBGT and regional requirements like Humidex-without changing how safety decisions should be made.