Mac storage basics · Checking your storage
How do I see the total size of several selected files or folders?
Short answer: Select the items and press Option-Command-I; the Finder Inspector shows their combined size. Command-I opens a separate window per item.
Select the items in Finder and press Option-Command-I to open the Inspector, which shows the combined size of everything selected. (Plain Command-I opens a separate Get Info window for each item.)
Finder's status bar also shows how many items are selected, but not their total size.