Some apps might be really 'heavy', so if you need to free up the storage, you might want to consider sacrificing a couple of them. Lucky for us, iOS and iPadOS have a function to analyze how much space each app uses.
There are few ways to check the storage on your device: Settings, iTunes, or the Finder on your computer.
Here is how you do it on your iPhone/iPad:
1) Launch Setting App > General > [Device] Storage;
2) Tap an app's name for more information about its storage.
Note, that cached data and temporary files might not be counted as usage.