Apple - Displaying combined file size of selected files in Finder

Instead of ⌘+I use ⌘+⌥+I to see the info:

Cmd+Ctrl+I does something similar, but gives you a static Summary Info window which doesn't update as your selection changes, and you can open multiple windows for different selections, which is handy for comparing groups of synced folders for example.

• Select the files
• right click
• hold alt (notice the menu options change)
• select 'Show Inspector'