Outlook View Folder Message Size: How to See It

To see the size of a folder in Outlook, right-click the folder in the navigation pane, select Properties, and click the General tab—the folder size appears under “Folder Size.” This shows both the total size of the folder and the size of just the items it contains, excluding subfolders. The same dialog also gives you the number of items in the folder, which helps you understand whether the size comes from a few large attachments or many small messages.

Why Folder Size Matters in Outlook

Every Outlook account has a storage limit, set by your email provider or your organization’s IT department. When you get close to that limit, you may be unable to send or receive mail, or the server may start deleting old items. Knowing the size of individual folders helps you find what is consuming the most space so you can archive or delete the right messages. This is especially important if you use Microsoft 365, where mailbox quotas are common, or if you have a free webmail account that offers only a few gigabytes.

How the Folder Size Dialog Works

The folder size dialog in Outlook (the same one used in Microsoft 365, Outlook 2021, 2019, and 2016) breaks the size into two numbers:

• Total size – the size of the folder itself plus all its subfolders.
• Subfolder size – the size of the folder’s subfolders only.

To get the size of just the folder’s own items, subtract the subfolder size from the total. The dialog also shows the number of items in the folder and its subfolders, which helps you spot folders with many small messages versus a few large ones.

Note that the size shown is the size on the server, not the size of your local Outlook data file (.ost or .pst). If you have a large local cache, the server size may be smaller because Outlook only stores a subset of messages locally.

Step-by-Step: View Folder Size in Outlook Desktop

1. Open Outlook and go to the navigation pane (left side) where your folders are listed.
2. Right-click the folder you want to check (for example, your Inbox or Sent Items).
3. Choose Properties from the context menu.
4. In the dialog that opens, click the General tab.
5. Click the Folder Size button near the bottom.
6. A new window appears showing the total size and the subfolder size. Write down the numbers if you need to compare folders.

If you want to see the size of all folders at once, you can use the Mailbox Cleanup tool: go to File > Tools > Mailbox Cleanup and click View Mailbox Size. This shows a breakdown by folder, but it only works for your primary mailbox, not for shared or archive mailboxes.

Viewing Folder Size in Outlook on the Web (OWA)

In Outlook on the web (the browser version), the process is slightly different:

1. Click the Settings gear icon in the top right.
2. Search for “mailbox” or go to Mail > General > Storage.
3. Here you’ll see a list of folders with their sizes and the number of items. The list is sorted by size, so the largest folders appear at the top.

This view is useful because it gives you a quick overview without opening each folder’s properties. However, it does not show subfolder sizes separately—each folder’s size includes its subfolders.

Common Problems and Misconceptions

One common misconception is that the folder size shown in Outlook is the size of the local .pst or .ost file. That is not true. The dialog shows the size of the items on the server. The local data file may be larger because it contains cached copies of all your messages, attachments, and other data.

Another issue: if you have a shared mailbox or a delegated mailbox, the folder size dialog may not show the size of that mailbox. You need to add the shared mailbox as a separate account in Outlook, or use the web version to see its storage usage.

If the folder size dialog shows 0 KB for a folder that clearly has messages, it could be due to a synchronization issue. Try restarting Outlook or using the web version to confirm the actual size.

How to Reduce Folder Size

Once you know which folders are large, you can reduce their size by:

• Deleting old messages that you no longer need, especially those with large attachments.
• Using the Mailbox Cleanup tool to find items larger than a certain size or older than a certain date.
• Archiving old items to a local .pst file or to an online archive if your organization provides one.
• Emptying the Deleted Items folder after deleting messages.
• Compressing attachments by saving them to a file share and removing the attachment from the email.

Remember that emptying the Deleted Items folder permanently removes the messages, so make sure you don’t need them.

Frequently Asked Questions

Why does the folder size show a different number than my mailbox size?

The mailbox size in Outlook’s status bar or the web version includes all folders, including ones you may not see (like the Recoverable Items folder). The folder size dialog only shows the folder you selected. Also, the web version may include the size of items in the cloud that are not cached locally.

Can I see the size of a folder in the Outlook mobile app?

No, the Outlook mobile app does not show folder sizes. You need to use the desktop or web version to see folder sizes.

Does the folder size include attachments?

Yes, the folder size includes all items in the folder, including messages, attachments, calendar items, and contacts. Attachments are a major contributor to large folder sizes.

Why is my Sent Items folder so large even though I don’t send many emails?

Sent Items often contains messages with large attachments. Every email you send is stored in Sent Items, and if you send files, those attachments are stored as well. Use the folder size dialog to see if the size is due to a few large messages.

How do I find the largest items in a folder?

In Outlook desktop, use the Mailbox Cleanup tool (File > Tools > Mailbox Cleanup > View Mailbox Size) and then click Find items larger than. You can specify a size threshold and Outlook will list all items above that size in your mailbox.

Is there a way to see folder sizes without opening each folder’s properties?

Yes, the web version of Outlook shows a storage summary under Settings > Mail > General > Storage. In the desktop version, you can use the Mailbox Cleanup tool to see a breakdown by folder. There is no built-in way to show sizes next to folder names in the navigation pane.

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