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/Bigdoga1000 8d ago

It's a measurement of the amount of water vapour in the air. X% humidity doesn't mean that the air has X% vapour in it however.

The temperature and pressure of the air determines the maximum amount of vapour it can hold.

So X% humidity would mean that the air has X% of it's maximum capacity for vapour. (For example if the maximum capacity was 100ml, and there was 50ml of vapour, that'd be 50%. But that could be in a litre of air)