Where did my Mac storage go?

macOS will tell you that your disk is full and roughly what kind of thing is filling it. It will not tell you which folder, which project, or which forgotten download. That last step is where all the space actually is.

Start with what macOS already knows

Open the Apple menu → System Settings → General → Storage. You get a coloured bar and a set of categories: Applications, Documents, macOS, System Data. It is a start, and it is also where most people get stuck, because the biggest slice is usually the vaguest one.

The categories lie a little, and here is why

Those categories are guesses based on file type and location. A 40 GB virtual machine image is a Document. An Xcode simulator runtime is System Data. A video project’s cache is Documents on one Mac and Other on another. The bar is not wrong exactly, but you cannot act on it.

What you actually need is a map

The question worth answering is “which folders are big, and how deep does that go”. Every disk analyzer exists to answer that. On a Mac you have a few ways to get it:

• Terminal, free: du -sh ~/* | sort -rh | head -20 lists your twenty largest top-level folders.
• Finder, free but slow: open your home folder, switch to list view, and sort by size — which only works inside one folder at a time.
• A disk analyzer: one scan, drawn as a map you can drill into.

The four places the space usually is

On most Macs, the answer is one of these, and it is worth checking them in this order.

1. Downloads. Years of installers, disk images and files you opened once. Sort by size, not by date.
2. Caches and logs, in ~/Library/Caches and ~/Library/Logs. Applications rebuild these; they can be cleared.
3. Developer leftovers, if you write software: Xcode derived data, iOS simulator runtimes, node_modules, Rust target folders, Docker images. These are routinely tens of gigabytes.
4. Large media you have already backed up: video projects, photo library duplicates, old exports.

About “System Data”

System Data is not one thing. It is the bucket macOS uses for everything it did not classify, and on a developer’s Mac it is usually simulator runtimes and derived data; on anyone else’s it is often caches, mail attachments and local Time Machine snapshots. There is a separate post about it.

One rule before you delete anything

Move things to the Trash rather than deleting them outright, and empty it a day later. Anything you needed will make itself known within hours, and restoring from the Trash costs nothing.

DiskDuo does this in one scan: a map of every folder, nine ways to read it, and a cleanup step that shows you each file before it moves it to the Trash. It is one payment, and it collects nothing about your files.

Download DiskDuo