This article describes how to compact the Personal Folders file(s) (PST) in
Microsoft Outlook, to eliminate deleted item space and recover room on your
To conserve space on your computer's hard disk, you can delete unwanted
items from the various PST folders and then compact the files to make them
: Deleting the unwanted items from each folder only moves them to the
Deleted Items folder, which is in the same file. You must delete the items
from the Deleted Items folder to permanently delete them, so that Outlook
can compact the file.
The compacting process does not remove all the free space from the file.
It leaves either 16 kilobytes (KB) or 4 percent of the file size (before
compacting) whichever is greater.
To be compacted, a file must meet the following requirements:
- The file must be 16 KB or larger.
- The file must have at least 16 KB of space freed since the last time
it was compacted.
You can start Outlook file compaction manually, or run it automatically in
Automatic Background Compaction
PST files that are not on your computer may require manual compaction, due
to interactions between the computer where the PST files are stored and
Automatic compaction takes place as an idle task in the background. The
following conditions must be true for this background task to take place:
- Outlook must be running.
- The computer must not be engaged in other CPU-intensive tasks such as
copying or downloading files.
To Manually Start PST Compaction
- If the Folder List is not showing, click Folder List on the View menu.
- Right-click one of the Personal Folders.
- Click "Properties For Personal Folders."
- On the General tab, click Advanced, and then click Compact Now.
- Click OK twice.