Guides · Storage guide
Two storage readings can disagree because they describe different things. Start by checking the destination volume, then distinguish free space from space macOS can reclaim. A failed operation needs a specific diagnosis, not another round of blind deletion.
Check the destination named by the failing app. An external drive, a disk image, a virtual machine, and the startup disk each have their own limits. Space available on your Mac does not create space inside a full disk image or on another drive.
Open Disk Utility and select the relevant volume. In Storage settings, use the available volume details to compare the same destination. A folder total, a volume total, and a container total answer different questions.
Available storage may include data that macOS can remove when needed. Purgeable content and local snapshots can therefore make the available figure larger than immediately unused storage. Apple specifically counts Time Machine snapshot space as available. Read Apple's explanation.
A failing app may also need temporary working space in addition to the final file size. Check that app's stated requirement and whether it writes temporary data to the startup disk. Do not assume the size of a download is its complete installation requirement.
You can list local Time Machine snapshots without changing them:
tmutil listlocalsnapshots /A list does not show the storage that deleting each snapshot would recover. Snapshots share blocks with live files and other snapshots. macOS normally handles their removal as storage is needed.
If you specifically need to remove local Time Machine snapshots, Apple documents temporarily setting the backup frequency to Manually and then restoring automatic backups after the snapshots have been removed. This discards those local restore points. Keep a current backup and follow Apple's current procedure.
APFS volumes in the same container share free space. APFS clones can share file contents too. Removing one file does not free blocks that are still referenced by another file or snapshot. Apple explains these APFS features.
For that reason, subtracting a folder's reported size from used storage is not a reliable prediction. Our APFS accounting article explains logical size, allocated size, and reclaimable space.
Delve can help identify the largest accessible folders on the volume you choose. Use the map to inspect real candidates, then recheck the volume after a reviewed cleanup. A visual scan complements the system's volume information; it does not replace it.
The tools may be measuring different volumes or using different definitions. Available space can include purgeable data, while another reading may show only immediately unused storage.
Usually let macOS manage them. Apple says their space is counted as available and reclaimed when needed. Removing snapshots also removes local restore points.
The files may still be in the Trash, or APFS blocks may still be referenced by other files or snapshots. Folder size is not a guaranteed deletion forecast.