How to compact the personal folders (.pst) files in Outlook

For a Microsoft Outlook 2000 (CW) version of this article, see
196990 .
For a Microsoft Outlook 98 (IMO) version of this article, see
179870 .
For a Microsoft Outlook 98 (CW) version of this article, see
179868 .


This article describes how to compact the personal folders (.pst) files in Microsoft Outlook, to eliminate deleted item space and recover room on your hard disk.

More Information

To conserve space on your hard disk, you can delete unwanted items from the various .pst folders, and then compact the files to make them smaller.

NOTE: When you delete the unwanted items from each folder, it 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 the background.

Automatic Background Compaction

Personal folders (.pst) files that are not on your computer may require manual compaction because of interactions between the computer where the .pst files are stored and your computer.

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.

How to Manually Start PST Compaction

  1. On the File menu, click Data File Management.
  2. Click the personal folders (.pst) files that you want to compact, and then click Settings.

    Note For Windows Vista, the default path of .pst files is drive:\Users\user\AppData\Local\Microsoft\Outlook. For Microsoft Windows XP or Microsoft Windows Server 2003, the default path of .pst files is drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook.
  3. Click Compact Now, click OK, and then click Close.