Relative Humidity

Relative Humidity

Relative humidity is the ratio, expressed as a percentage, of the amount of water vapor in the air compared to the maximum amount the air could hold if it were fully saturated at that temperature. Because the saturation point depends on temperature, relative humidity reflects a combination of both temperature and moisture content. It is calculated using the air temperature and dew point for a given time.

Relative humidity can be deceptive. For example:

• At a temperature of 30°F with a dew point of 30°F, the air is saturated, and relative humidity is 100 percent.
• At a temperature of 80°F with a dew point of 60°F, the relative humidity is only 50 percent.

Even though the first case shows 100 percent humidity, the second case feels much more humid. That’s because the dew point is higher, meaning the air actually contains more water vapor. For gauging how humid or muggy it will feel outdoors, the dew point is a more reliable indicator than relative humidity. The higher the dew point, the heavier and more uncomfortable the air will feel.

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Relative Humidity

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