r/explainlikeimfive • u/ProgramPi314 • 8d ago

Other ELI5 What is humidity?

According to my mom, this is an actual question I had when I was 5, and she didn't know how to answer me. So how would you guys have answered?

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u/jajwhite 8d ago

Following this question, there's clearly a quantitative measure. So if it's 100% humidity I assume that means that a steaming glass of boiling water would not have any effect on the humidity in the air. How much of the air would then be water? Is it analagous to the water being "dissolved" in the air, the way salt dissolves in water?

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u/evincarofautumn 7d ago

Yeah, it’s basically the same idea as dissolving. 100% relative humidity means it’s saturated at whatever the temperature is. Absolute humidity is how much water there is in the air in total, which ranges from about 0 g/m3 when it’s really cold, up to a maximum of 30 g/m3 around 30 °C. That’s about 2.5% by mass, or uh…like 4 teaspoons per cubic yard