How to Measure Humidity

Humidity

How to Measure Humidity

 

Humidity is the amount of water vapor (or moisture) in air. There are various ways to

measure and state the level of humidity. The two common ways to measure humidity are

Absolute Humidity and Relative Humidity. In this article we look at these common ways of

measuring humidity, understand the difference between them and see their relevance to our

daily lives.

 

Let’s start with Absolute Humidity. As the name suggests, this is simply a measure of the

amount of water contained by a unit of dry air. As air is a mixture of gases, the unit of air is

expressed as volume. The Absolute Humidity is then expressed as the mass of water

contained by the unit volume of air, i.e. grams of moisture per cubic meter of air. The

Absolute Humidity in the air can range anywhere from 0 to 30 grams per cubic meter.

 

Because the characteristics of air change according to the temperature and pressure, the

limits of moisture it can contain also changes accordingly. Cool air can contain lesser

maximum moisture than warm air. As the moisture reaches the maximum level, it turns into

water. This, by the way, is also how rain starts in the clouds. As the temperature of air

increases, the amount of moisture needed to form water increases. This is also partially the

reason why the chances of rain are greater in colder weather, even with the same amount of

cloud cover.

 

The next common measure of humidity is the Relative humidity. Commonly, when reading

the weather reports, the humidity levels stated are actually Relative Humidity. As opposed

to the Absolute Humidity, Relative Humidity is a percentage measure. It is the comparison

of Absolute Humidity at a particular temperature to the highest possible Absolute Humidity at

that temperature. This makes it easier to compare humidity levels and avoids the necessity

to remember the maximum possible humidity level at different temperatures.

 

The Relative Humidity is a commonly used measure. Even the recommended humidity

levels of 30% to 50% are actually recommended Relative Humidity levels. Some electronics

come with a range of humidity levels they can operate in. This is also a range of Relative

Humidity. The effect of humidity on a property is also better correlated to Relative Humidity. It

is when either the moisture in the air starts turning to water, starts to condensate on the cold

surfaces or wet surfaces cannot get dry, that property starts to get damaged by the humidity.

All these issues relate to the air reaching its maximum capacity of containing moisture.

 

The effect of humidity on the perception of temperature is also better correlated with the

Relative Humidity. When the Relative Humidity is at or close to 100%, the sweat from our

bodies cannot evaporate. This makes it difficult for the body to lose heat. As a result, our

bodies produce more sweat and we feel increasing levels of heat and discomfort. The

temperature feels more than it actually is. Contrary to that, when the Relative Humidity is

close to 0%, then the sweat evaporates very quickly and the body starts losing heat more

than it wants to. This makes the temperature feel less than actual. This variance in

perceived temperatures can easily be up to 10 degrees Fahrenheit from the actual temperature. Interestingly, High Relative humidity can decrease the chill felt during cold

weather and low Relative Humidity can decrease the perception of heat during hot weather.

 

As stated earlier, a Relative Humidity from 30% to 50% works well for people as well as

property. At this level of Relative Humidity, we don’t feel unnecessary or additional

discomfort. Of course, a very high or low temperature within the recommended Relative

Humidity range will still be uncomfortable. In areas with drier than usual climates, people

tend to use humidifiers to maintain appropriate levels of Relative Humidity. On the other

hand, in areas with wet climates, people tend to use dehumidifiers to maintain a healthy level

of Relative Humidity.

 

We hope you liked this introduction to humidity and how it is measured. We presented an

easy to understand definition of Absolute and Relative Humidity and how they are related to

each other. We summarised how Relative Humidity is a more relevant measure and why it

is important for our everyday lives.

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Keywords: absolute humidity, relative humidity, ideal humidity range, dry climate, wet climate

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