One folder: Get Info
Select the folder and press ⌘I (or right-click › Get Info). The Size line shows bytes on disk and the number of items. Big folders take a few seconds to calculate.
For a live view, open the Inspector with ⌘⌥I instead: it updates as you click different folders.
Every folder in a window: list view
- Switch to list viewPress ⌘2 in the Finder window.
- Open View OptionsPress ⌘J.
- Tick Calculate all sizesFolder sizes appear in the Size column. Click the column header to sort by size.
- Optional: Use as DefaultsApplies the setting to every Finder window.
Calculate all sizes slows Finder on folders with thousands of items, because it re-measures each time you open the window.
In Terminal
Size of one folder, then every folder inside your home folder sorted biggest last:
du -sh ~/Downloadsdu -hd1 ~ 2>/dev/null | sort -hTerminal needs Full Disk Access (System Settings › Privacy & Security) to measure Mail, Messages and some Library folders; otherwise those show as permission errors.
Every folder on the disk at once
Get Info and du both re-measure each time. Broom scans the disk once (1.78 million files in 8.4 seconds on an M4 MacBook Air) and then shows every folder's size instantly. Click into any folder to go deeper, or switch to a treemap or sunburst to see proportions at a glance.
Questions
Why doesn't Finder show folder sizes?
Measuring a folder means reading every file inside it, which is slow. Finder only does it when you ask: Get Info, or Calculate all sizes in View Options.
Why are size and size on disk different?
Size on disk counts whole storage blocks, and APFS clones and compressed files can use less than their logical size.
What's the fastest way to find the biggest folders?
A disk space analyzer. Broom shows every folder sorted by size after one scan.