Apps · The Apps window and launcher
How do I see how much space an app's data and caches use?
Short answer: Right-click the app in the All Apps grid: the menu shows where the app and its data and caches live, with sizes. The Uninstall screen lists each piece too.
Right-click the app in the All Apps grid. The bottom of the menu shows where the app itself lives and where its data and caches live, each with its size — highlighted when it's on your Mac (space you could reclaim) and greyed when it's on your fast drive.
The Uninstall confirmation also lists each piece of an app's data with its size.