What Humidex describes
Combine Celsius temperature and dew point into the Canadian humidex index.
Humidex is a dimensionless Canadian index commonly expressed like a Celsius temperature. It describes combined heat and moisture, but it is not an actual thermometer reading. Its value comes from a defined weather record rather than from the title alone, so the source interval and location should travel with the answer.
The visible input set for Humidex is air temperature, dew point. Before entering them, decide whether the record represents an observation, a forecast scenario, or a historical comparison. That choice changes how humidex should be described even though it does not change the arithmetic.
Time and location boundaries for Humidex
Define where the Humidex observation applies and when its interval begins and ends. Local terrain, shade, surface type, urban development, elevation, and distance from water can create real temperature differences over short distances.
If the intended decision concerns another site, avoid treating the nearest available station as automatically representative. Document the distance and exposure difference beside humidex and explain why the source is suitable.
The working rule behind Humidex
The page applies T + 0.5555 × (vapor pressure − 10), using dew point. Only the visible entries participate in the calculation; it does not silently retrieve a station observation, forecast, elevation, or climate normal.
For Humidex, keep intermediate precision until the final display. If another source uses a different formula or convention, label both methods before comparing their answers.
From Humidex, a connected temperature question can be explored with the Growing Degree Days Calculator.
Units, signs, and sensible magnitude
Humidex reports an index value. Carry the input units through the formula and preserve the sign when it communicates direction. Converting only one entry can produce a plausible-looking but unusable result.
Estimate the order of magnitude of humidex before accepting the display. A relevant boundary case—equal temperatures, zero duration, the selected base, or a calm condition where permitted—can expose a reversed subtraction or misplaced factor.
Using Humidex in context
One Humidex value establishes a weather summary, not a trend. Repeated results become comparable only while their collection and calculation methods remain aligned.
When humidex feeds another model, transfer its unrounded value together with units and assumptions. Round only at the reporting stage and only as finely as the source observations support.
Keeping the weather record auditable
Save the raw observations as well as the displayed humidex. Record conversions, rounding, missing-data treatment, and the reason this calculation was performed so another person can reproduce it without guessing.
Create a new dated Humidex result when the location, observation window, instrument, formula convention, or source value changes. Overwriting the earlier calculation removes the evidence needed to explain a later difference.
Comparing two Humidex records fairly
Before ranking two results, align their units, observation windows, sensor exposure, quality control, and calculation convention. A difference in humidex may come from method rather than weather.
Keep the original Humidex observations visible during comparison. Converting, averaging, and rounding both records through the same documented route makes a real difference easier to distinguish from processing noise.
What the Humidex result leaves out
Humidex is not interchangeable with the U.S. heat index or Australian apparent temperature. It does not diagnose heat illness and should not be treated as a personalized safe-exposure limit.
Humidex supplies transparent arithmetic, not a forecast, warning, diagnosis, engineering certification, or permission to enter hazardous conditions. Current official information and the rules governing the activity take priority.
Sensitivity to the least certain input
Identify the observation with the greatest uncertainty and rerun the calculation at credible low and high values. The spread shows whether measurement quality could change the practical interpretation of humidex.
Do not present the Humidex sensitivity range as a confidence interval unless input uncertainty was estimated statistically. This is a controlled check of the formula, not a probability forecast.
Choosing observations for Humidex
Temperature and dew point should represent the same place and time. Because the formula derives vapor pressure from dew point, an inconsistent or stale dew-point observation can dominate the result.
A reproducible Humidex record retains the station or sensor identifier, observation time, time zone, height or exposure when relevant, and any quality flag. Without that context, the number can look precise while describing the wrong interval or place.
A reproducible example and independent check
The starting values shown in the form provide a complete test case. Calculate them once by hand with T + 0.5555 × (vapor pressure − 10), using dew point, then change one input whose effect is predictable and confirm that the answer moves in the expected direction.
After testing Humidex, replace every sample value with one internally consistent weather record. Reset restores this demonstration; it does not retrieve data from an external weather service.
Reading the calculated Humidex
Use established Canadian humidex guidance when interpreting ranges. Individual response still depends on exertion, health, acclimatization, clothing, sun, wind, and access to cooling.
Compare humidex with a relevant observation, forecast, normal, or operating threshold selected before using Humidex. Choosing the benchmark afterward can exaggerate an ordinary difference.
From Humidex, a connected temperature question can be explored with the Temperature Inversion Strength Calculator.
Questions about Humidex
What does Humidex calculate?
It calculates humidex from the entries and the displayed rule, reporting an index value.
Can I enter forecast values?
Yes, but label the Humidex result as a scenario. Do not mix a forecast input with an observation without documenting the difference.
Why might another source give a different answer?
Another Humidex source may use a different observation interval, station, rounding rule, threshold, formula variant, or unit convention.
How should I check the result?
Repeat T + 0.5555 × (vapor pressure − 10), using dew point independently, keep full intermediate precision, and test one input change with an obvious direction.
When should I calculate it again?
Create a new Humidex result when an input, observation period, location, instrument, or formula convention changes.