How to use the Humidex

About the Humidex

The Humidex is a tool we use to describe how hot, humid weather feels to the average person. It combines the air temperature and relative humidity into one number, that reflects the perceived temperature.

A Humidex reading can help you make informed decisions about outdoor activities and heat-related health risks.

Use the Humidex calculator to get the reading in your area.

When we use the Humidex

We include the Humidex reading when we share current conditions, weather forecasts, and heat warnings in areas where there is humidity during hot weather.

For 24-hour forecasts:

when the temperature reaches 25°C or higher and
the Humidex is at least one degree higher than the temperature

For current conditions:

if the temperature is currently 20°C or higher and
the Humidex is at least one degree higher than the temperature

Understanding Humidex readings

We categorize Humidex readings into four separate ranges of temperatures, grouped by their level of impact. The ranges start from the lowest level of discomfort and risk to your health and increase to the highest level of discomfort and level of risk.

Keep in mind, some people will be more affected by Humidex than others.

First Humidex range:

20 to 29
little discomfort

Second Humidex range:

30 to 39
some discomfort

Third Humidex range:

40 to 45
great discomfort; avoid exertion

Fourth Humidex range:

above 45
dangerous; heat stroke possible

Humidex and your health

For a Humidex reading above 30, you should limit or modify outdoor exercise, depending on:

your age
individual physical limitations
the type of clothes you are wearing, and
other weather conditions

Any Humidex value over 40 is an extremely high Humidex reading. At that point, you should reduce all unnecessary physical activity.

Extremely high readings of the humidex are rare except in the southern regions of Ontario, Manitoba, and Quebec.

How we calculate the Humidex

The Humidex level is based on air temperature and percent of humidity in the air. For example, if the air temperature is 21 degrees Celsius outside, but the air humidity is at 100%, then it will actually feel like 29 degrees Celsius on your skin. Therefore, the Humidex rating is 29.

The Humidex table

The Humidex table is a tool that shows the Humidex levels from combinations of different air temperatures and percentages of humidity.

Table 1 Reference legend for Humidex range and degree of comfort
Humidex	Degree of comfort
20 - 29	Little discomfort
30 - 39	Some discomfort
40 - 45	Great discomfort; avoid exertion
46 and over	Dangerous; possible heat stroke

Table 2 Humidex for relative humidity from 100% to 65%
Use the legend in Table 1 to estimate degree of comfort for each Humidex level.
Relative humidity (%) Temperature (°C)	100%	95%	90%	85%	80%	75%	70%	65%
21 °C	29	29	28	27	27	26	25	24
22 °C	31	31	30	29	28	28	27	26
23 °C	33	33	32	31	30	29	28	28
24 °C	35	34	34	33	32	31	30	29
25 °C	37	36	35	35	34	33	32	31
26 °C	39	38	37	37	36	35	34	33
27 °C	42	41	40	39	37	37	35	34
28 °C	44	43	42	41	39	38	37	36
29 °C	46	45	44	43	42	40	39	38
30 °C	49	47	46	45	44	42	41	40
31 °C	51	50	48	47	46	44	43	42
32 °C	54	52	51	49	48	47	45	44
33 °C	56	55	53	52	50	49	47	46
34 °C	59	57	56	54	53	51	50	48
35 °C	-	60	58	57	55	53	52	50
36 °C	-	-	61	59	58	56	54	52
37 °C	-	-	-	-	60	58	56	55
38 °C	-	-	-	-	-	-	59	57

Table 3 Humidex for relative humidity from 60% to 20%
Use the legend in Table 1 to estimate degree of comfort for each Humidex level.
Relative humidity (%) Temperature (°C)	60%	55%	50%	45%	40%	35%	30%	25%	20%
21 °C	24	23	22	22	-	-	-	-	-
22 °C	25	25	24	23	-	-	-	-	-
23 °C	27	26	25	24	24	-	-	-	-
24 °C	28	28	27	26	25	24	-	-	-
25 °C	30	29	28	27	26	26	-	-	-
26 °C	32	31	30	29	28	27	-	-	-
27 °C	33	32	31	30	29	28	27	-	-
28 °C	35	34	33	32	31	30	29	-	-
29 °C	37	36	35	33	32	31	30	-	-
30 °C	39	38	36	35	34	33	32	30	-
31 °C	41	39	38	37	35	34	33	32	-
32 °C	42	41	40	38	37	36	34	33	-
33 °C	44	43	42	40	39	37	36	34	-
34 °C	46	45	43	42	40	39	37	36	-
35 °C	48	47	45	44	42	40	39	37	-
36 °C	51	49	47	46	44	42	40	39	-
37 °C	53	51	49	47	46	44	42	40	-
38 °C	55	53	51	49	47	45	44	42	40
39 °C	57	55	53	51	49	47	45	43	41
40 °C	-	57	55	53	51	49	47	45	43
41 °C	-	-	58	55	53	51	48	46	44
42 °C	-	-	-	57	55	53	50	48	46
43 °C	-	-	-	-	57	54	52	50	47

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