Mac storage basics · Finding big files, Downloads and the Trash
How do I make a Smart Folder that always shows my biggest files?
Short answer: Choose File → New Smart Folder, add a File Size is greater than criterion, then Save and add it to the sidebar. It updates itself from Spotlight's index.
In Finder choose File → New Smart Folder, click +, set the criterion to File Size (via Other… if it isn't listed) and is greater than a size you choose, then click Save and tick Add To Sidebar.
The folder updates itself, so it's a quick way to keep an eye on large files without searching each time. It only shows files Spotlight indexes.