How to check storage on your Mac

1. System Settings

1. Open the Apple menuChoose System Settings.
2. Go to General › StorageThe bar at the top shows used and available space by category.
3. Wait for it to finishCategories like System Data fill in last. Click the ⓘ next to a category for its biggest items.

On macOS Monterey and earlier: Apple menu › About This Mac › Storage.

2. Finder

Select your disk in the Finder sidebar (or the desktop) and press ⌘I. Get Info shows Capacity, Available and Used. To keep it visible, turn on View › Show Status Bar in any Finder window: it shows free space at the bottom.

3. Disk Utility

Open Applications › Utilities › Disk Utility and select your startup volume. It shows Used, Free and the APFS container the volume shares space with. Useful when you have several volumes or partitions; it says nothing about which files use the space.

4. Terminal

The quickest exact number:

df -h /

diskutil info / | grep -E 'Container (Total|Free) Space'

df on an APFS volume shows space shared by every volume in the container. That's why it can disagree with Finder. More commands in check disk space in Terminal.

Why the numbers don't match

• Purgeable space. Finder counts space macOS can free on demand (iCloud copies, snapshots, caches) as available. df doesn't. See purgeable space on Mac.
• GB vs GiB. macOS uses 1 GB = 1,000,000,000 bytes; some tools use 1 GiB = 1,073,741,824. A 500 GB disk shows as 465 GiB. Try the storage converter.
• Shared APFS containers. All volumes on a disk share one pool of free space.

See what's inside, not just how much

None of the built-in tools tell you which folders are big. Broom scans the disk with Full Disk Access and shows every folder by size as a list, sunburst, treemap or flame graph, so the 40 GB folder you forgot about stands out immediately.