Performance & battery · Why background work waits or pauses
Why are folder sizes taking a while to appear in Storage Studio?
Short answer: Measuring a folder means reading everything inside it, so Storage Studio does it gently in the background and lets your work go first. Unmeasured folders show a spinner, never zero, and fill in over time.
Working out a folder's real size means reading through everything inside it, so Storage Studio does it quietly in the background and lets your own work go first. Sizes fill in from the top of the list as they're worked out, faster when you leave the Mac alone.
A folder that hasn't been counted yet shows a spinner, never a zero — so an unmeasured folder can't be mistaken for an empty one before you move it. When sorting by size, unmeasured folders sort to the end.
If you want it done sooner, leave the Mac idle and plugged in for a bit. Related: Does indexing work like Spotlight?