What this calculator does

This humidex calculator estimates how hot the air feels by combining air temperature with moisture using the Environment and Climate Change Canada humidex framework. It is especially useful for warm-season communication where humidity materially changes comfort and health risk.

Humidex is similar in purpose to heat index, but it is built from a different equation and is commonly used in Canadian weather communication. Because the index ties the moisture burden to vapor pressure through dew point, it offers a helpful way to express why a humid day can feel much hotter than the thermometer suggests.

Inputs explained

• Air temperature: Enter the current dry-bulb air temperature.
• Dew point temperature: Enter the dew point so the calculator can estimate the moisture contribution directly.
• Unit handling: The page calculates in Celsius internally and can present the interpreted result cleanly for users.

How it works / method

The page first converts dew point to vapor pressure using the standard Environment Canada style relationship. It then computes a humidex adjustment term and adds that term to the air temperature. The final value is not a direct air temperature replacement; it is a comfort and risk index for hot and humid weather.

Formula used

T and Td are handled in C. The dew point drives the vapor pressure term, which then raises the apparent heat burden above the dry-bulb air temperature.

Step-by-step example

Suppose the air temperature is 30 C and the dew point is 24 C. The humidex value helps communicate how heavy and oppressive the air may feel.

1. Enter 30 for air temperature.
2. Enter 24 for dew point.
3. The calculator converts dew point to vapor pressure and computes a humidex in the upper 30s or low 40s.
4. That range points to noticeable discomfort and a stronger need for hydration and reduced exertion.
5. If dew point drops while temperature stays the same, humidex usually falls quickly.

Use cases

• Explaining Canadian-style warm-weather comfort messaging in forecasts or preparedness content.
• Comparing hot days where the thermometer value is similar but the dew point is very different.
• Helping users move from raw moisture metrics such as dew point to a more intuitive heat-burden scale.
• Supporting outdoor planning when humidity is the main reason the weather feels oppressive.

Assumptions and limitations

• Humidex is built for warm and humid weather and should not be interpreted as a physical air temperature measurement.
• The result depends on the dew point estimate or measurement, so poor humidity inputs will propagate into the final value.
• It does not directly account for solar radiation, terrain, personal heat generation, or formal occupational exposure standards.
• Different regions may communicate heat stress with different indices, so humidex is not the only valid framework.

If you need a sun-sensitive screening metric, compare humidex with WBGT. If you want a direct moisture indicator, look at the dew point page instead.

Sources & references

• NOAA National Weather Service - Heat index guidance
• NOAA National Weather Service - Wind chill chart and formula
• NOAA National Weather Service - Wet Bulb Globe Temperature overview
• Bureau of Meteorology - Apparent temperature background
• Bureau of Meteorology - Apparent temperature glossary
• Environment and Climate Change Canada - Humidex guidance
• Schema.org - FAQPage and WebApplication vocabulary