Here's a helpful guide on checking the mailbox size across different Outlook versions and understanding how it compares to .pst and .ost file sizes.

Running short on storage in Outlook can result in various problems, such as sluggish performance due to large data files or being unable to send and receive emails once your mailbox hits its limit. Monitoring your mailbox size allows you to preemptively address storage limitations, providing ample time to clear out unnecessary emails and maintain smooth Outlook operation.

To view the size of your mailbox in the classic Outlook application, follow these steps:

1. Open Outlook and select the root folder of your mailbox / account – this is typically your email address.

2. Navigate to the Folder tab and click Folder Properties.

3. Within the Properties window, under the General tab, click Folder Size.

4. The Folder Size window will display the total storage used by your mailbox and its subfolders.

   • By default, Outlook shows Local Data (stored in a .pst or .ost file on your computer).
   • To check the size of your mailbox on the server, switch to the Server Data tab and wait for Outlook to fetch the information.

   

Another method to get mailbox size in Outlook

Another quick way to see your mailbox size and how much space each folder takes is via the Mailbox Cleanup tool:

1. In Outlook, go to the File tab.
2. Click Tools, and then select Mailbox Cleanup.
3. In the Mailbox Cleanup dialog box, click View Mailbox Size.
4. A pop-up window will display your total mailbox size, along with a breakdown of each folder's storage, both locally and on the server, just like the Folder Properties option.

Tip. Outlook shows mailbox size in kilobytes (KB). To convert to megabytes (MB), use one of these methods depending on how much precision you need:

• Quick estimate: Shift the decimal point three places to the left (divide KB by 1000) for an approximate conversion. For instance, if your mailbox is5608 KB, it would be ≈ 5.6 MB.
• Precise calculation: Divide the number of kilobytes by 1024. For example, 5608 KB / 1024 = 5.4765625, which is about 5.48 MB or 5.5 MB.

How to view size of mailbox in new Outlook and web

In the new Outlook and Outlook on the web (for work and school accounts), checking the mailbox size and available storage is done as follows:

1. Click the Settings gear icon in the top-right corner.
2. In the left pane, select Accounts > Storage.
3. If you have multiple accounts added to the new Outlook, pick the one you're interested in from the drop-down menu at the top.
4. In the right pane, under Storage, you'll see the total mailbox capacity and the amount currently used.
5. Under Manage Storage, you'll find a breakdown of how much space each folder in the selected mailbox is using.

Note. Storage settings are not available for third-party email accounts like Gmail or Yahoo integrated into the new Outlook.

How to check if mailbox is full in Outlook.com

To determine if your mailbox is approaching its storage capacity in Outlook.com, follow these steps:

1. Log into your Outlook.com account in a browser.
2. Click Settings > Accounts > Storage.
3. At the top of the Storage section, you'll see your total available Microsoft storage, including files, photos, and email attachments across your Microsoft account, including OneDrive.
4. Under Email Storage, you'll find your mailbox limit.
5. To check how much space is used, click the down arrow next to Email storage to expand the section. This will show a breakdown of storage usage by folder.

Note. For Outlook.com accounts added to the new Outlook, the storage settings are displayed in a similar way.

These methods help you monitor your mailbox usage and manage storage effectively. If your mailbox is nearing its limit, consider deleting unnecessary emails, archiving old messages, or moving large attachments to an external location.

How to find Outlook PST and OST file size

Microsoft Outlook stores users' mailboxes including emails, calendar items, tasks and other data in one of these files:

• PST (Personal Storage Table) – used by POP accounts to store mailbox data locally.
• OST (Offline Storage Table) – used by IMAP and Exchange accounts to enable offline access to mailbox data.
• NST (also known as Group Storage Table or GST) – used in Outlook 365 to store group data.

You can check the size of these files through their properties, just like any other file on your computer. The key step is knowing where to find them.

Default location of Outlook PST and OST files

The location of Outlook data files varies by version and Windows operating system.

Outlook 365, 2019, 2016, and 2013

• Windows 11, Windows 10, and Windows 8: C:\Users\<username>\AppData\Local\Microsoft\Outlook</username> or C:\Users\<username>\Roaming\Local\Microsoft\Outlook</username>
• Windows 7 and Windows Vista: C:\Users\<username>\Documents\Outlook Files</username>

Outlook 2010

C:\Users\<username>\Documents\Outlook Files</username>

Outlook 2007 and earlier

C:\Users\<username>\AppData\Local\Microsoft\Outlook</username>

Older Windows and Outlook versions

C:\Documents and Settings\<username>\Local Settings\Application Data\Microsoft\Outlook</username>

C:\Users\<username>\Documents\Outlook Files</username>

C:\Users\<username>\My Documents\Outlook Files</username>

Note. The AppData folder is hidden by default. To make it visible, you can either:

• Open File Explorer, click View in the top menu, and select Show > Hidden items.
• Go to Control Panel > File Explorer Options > View tab, then select the Show hidden files, folders, and drives option under Hidden files and folders.

How to determine the location of .pst or .ost file on your computer

Given that different Outlook versions store files in various locations, the simplest way to locate your Outlook data file is this:

1. Click File > Account Settings > Account Settings.
2. In the Account Settings dialog box, switch to the Data Files tab.
3. Select a desired account, and click Open File Location…

This will open File Explorer, showing the folder where your Outlook data file is stored.

How to check Outlook PST and OST file size

After locating your Outlook data file, you can check its size in this manner.

1. Open the folder containing .pst or .ost in File Explorer.
2. Switch to Details view to see the file sizes listed in the Size column. This is particularly useful if you have multiple Outlook accounts, as each mailbox stores data in

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