Imagine that it's a cold autumn morning, 40 ☏ outside (~4.5 ☌).To better understand the difference between dew point and humidity, let's look at this example: In a particular case, when the air is maximally saturated with water (the relative humidity is 100%), the dew point is equal to the current temperature. Relative humidity is a more confusing value as it depends on temperature and the pressure of the system in question.ĭew point and relative humidity are not the same, but they are closely related: the higher relative humidity is, the closer the dew point is to the current air temperature. If you want to know whether (or weather, heh) it's comfortable or not to have a morning jog or go on a weekend hiking trip – stick with that term. The higher the dew point is, the more moisture that is in the air. Now that you know the formulas for dew point and humidity, you may wonder, what is the difference between those two terms?ĭew point is an accurate measurement of the moisture content in the air. It is merely the water content in the air, expressed in grams per cubic meter:Ībsolute humidity = m / V, where m is the mass of water vapor, and V is the volume of the air and water vapor mixture.įor saturated air at 30 ☌ (86 ☏), the absolute humidity in the atmosphere ranges from ~0 to 30 grams per cubic meter.ĭid you notice that the formulas don't take the temperature into consideration? To understand this definition, you also need to know the meaning of absolute humidity.
Or, expressed differently, the relative humidity is the ratio of the water vapor pressure Pw to the saturation water vapor pressure Pws at the given temperature:
In other words, it's the amount of moisture in the air compared to what the air can maximally "hold" at that temperature: It is the ratio of the current absolute humidity to the maximum absolute humidity possible for the current temperature. Relative humidity is expressed as a percentage.
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