Mac storage basics · Finder tools for finding space
How do I show how much free space is left at the bottom of Finder windows?
Short answer: Choose View → Show Status Bar in Finder. The bottom of each window then shows the item count and the space available on that folder's disk.
Turn on Finder's status bar: choose View → Show Status Bar (Command-/). Every window then shows, along the bottom, how many items are in the folder and how much space is available on the disk that folder lives on.
Open a folder on an external drive and the bar shows that drive's free space instead, which makes it a quick way to compare disks. The figure Finder shows counts space macOS can free on demand, so it can be higher than other tools report — see why Finder and Storage settings disagree.