This article explains how to check the size of folders and subfolders in Outlook. This is useful because Outlook can become slow when folders accumulate large emails and attachments. Identifying which account is using the most space, as well as the subfolders containing large files, can help you delete unnecessary data. Instructions apply to Outlook 2019, 2016, 2013, 2007; and Outlook for Microsoft 365.

To view the size of your folders in Outlook:

Right-click on the folder you want to check and select Data File Properties. In Outlook 2019, select Properties.

The Folder Size dialog box displays the size of the folder and its subfolders in kilobytes.