Relative Humidity Lesson for Kids

Instructor: Patrick Zedrow

Patrick has taught intermediate science, language arts, and technology. He has a master's degree in educational technology.

On a hot summer day, a lot of people check the temperature outside. Have you ever noticed another little number right next to it that looks like a percentage? This is called relative humidity, and it can tell you much more about how it feels outside.

What is Humidity?

Did you know that water is in the air right now? The air is full of these tiny water particles floating around, called water vapor. Humidity is the amount of water vapor in our air. When there is a lot of water vapor in the air, you could say that the humidity has risen. This is true in rainforests and places near the ocean. Now, think of some places where humidity is low - you might imagine a desert or some other dry area. Humid places can feel sticky and muggy. Humidity can change often, and it can always be measured.

What is Relative Humidity?

One way we measure the amount of water in our air is called relative humidity. Remember, the word ''relative'' means ''compared to.'' So, relative humidity is how much water is in the air compared to the temperature of the air. It is written as a percentage; when the relative humidity is, say, 50%, that means the air is holding half the amount of water that it actually could hold.

Hot air has the most holding power, similar to how classroom 3 can hold the most students.

Hot vs. Cold

Here's an interesting fact: hot air can hold more water than cold air. Think of a blob of cold air as a small cup of water. A blob of hot air is like a huge bucket! So a relative humidity of 50% is totally different on a hot summer day compared to a cool autumn day. The summer air is like the big bucket, and the autumn air is like the small cup. In fact, the autumn air could have an RH of 90%, and there still wouldn't be as much water in the air as summer air with an RH of 50%! So the next time you hear someone say, ''The relative humidity is 100% today,'' that doesn't necessarily mean it will feel really sticky outside. You must first consider what the temperature is.

If the air was a container, the hot air would be much bigger than the cold air because it can hold more water.

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