How to Increase the Size Limit of PST and OST Files

Updated On - December 23, 2023 by Henry Bray | Reading Time: 5 minutes

The size limit is always a matter when you are dealing with large files. As a result, many times we get emails with large attachments and, as a result, our PST files become larger. However, it is a minor issue, but it creates more errors. As usual, when users start receiving errors due to the increase in the maximum size of PST files, they seek possible solutions. In this article, we will talk about how to increase the maximum size for PST-files and OST-files in Outlook. Keep reading

Before starting, let’s learn a little about the default size for PST and OST files in Outlook

Actually, there is a default or suggested maximum size for non-Unicode PST and OST files in all Outlook versions, which is 2 GB. But the maximum recommended size for Unicode PST and OST files is not specific to all versions of Outlook. It varies depending on the version.

Generally, the MS Outlook 97–2002 version has a file size restriction of 2 GB and produces non-Unicode (ANSI format) files. If you are using Outlook 2003 and 2007, you have a storage limit of 20 GB, and for Outlook 2010, 2013, 2016, and 2019, the maximum recommended size or storage limit is 50 GB.

The Outlook data file has reached the maximum size

Manual method to increase the maximum size for PST and OST files in Outlook

Because the default size for PST and OST files is restricted, users may want to increase the size. It is possible to do so using the Registry Editor, which allows you to increase the size up to about 4PB (which is almost 4096 TB), depending on the versions of Outlook.

But before going forward, we want to inform you that this process isn’t workable for the PST and OST files of the Outlook 97-2002 versions that use non-Unicode (ANSI format) files.

What to do in the Registry?

Simply make two simple registry changes for increasing OST and PST file size (in the locations listed below). As the desired directory is not specific to all Outlook versions, we have mentioned multiple locations. Find your version and go to the location.

Microsoft Outlook 2003

Microsoft Outlook 2007

Microsoft Outlook 2010

Microsoft Outlook 2013

Microsoft Outlook 2016/ 2019 and Microsoft 365

After going to the location according to your Outlook version, you need to set two new DWORD values.

1. WarnLargeFileSize: [Note: Set it no higher than “4090445042” (decimal) or “f3cf3cf2” (hexadecimal)]

2. MaxLargeFileSize: [Note: Set it no higher than “4294967295” (decimal) or “ffffffff” (hexadecimal)]

increase the maximum size for PST and OST files

Actually, the first number (WarnLargeFileSize) specifies how many megabytes (MB) a user can write to a pst-or ost-file before receiving an alert that the file is overflowing. You can see in the above picture, it is set to 95 GB.

The second parameter (MaxLargeFileSize) specifies how many megabytes (MB) the system may write to a pst or ost file. Because there is more written to a pst-file and an ost-file rather than user data, this difference must be at least 5%. In the above picture, it is set to 100 GB.

Use professional software to solve the large PST file size issue in Outlook

Usually, if you have hit the size limit in Outlook, you will start getting errors like sending or receiving errors, PST file corruption, etc. In this regard, the best and easiest solution for you is to delete some unwanted items and instantly get more free space.

But when you are attempting to delete files, you realize that all the files are important to you and you can’t lose them. Besides, you don’t have any backup. In this situation, you can increase the maximum size for PST-files and OST-files (this manual process is described above) with the Registry Editor.

Through the Registry, you can effectively solve the issue, but because of its critical steps, many users seek professional solutions. Now the question is, is there any third-party software that can solve the large file issue in Outlook? The answer is yes.

We will talk about the Regain PST Splitter software. Actually, it can’t do any setup that automatically increases the file size limit in Outlook’s settings or do any miracle that enlarges Outlook’s volume. But it has the functionality that can split the large PST files into small ones. And in this way, the size limit for PST files can be maintained without making any changes to the settings.

Free Download100% Secure Buy NowPrice: $29

Let’s see how the Regain PST Splitter software works step-by-step.

  1. Firstly, you need to install the program on your computer or laptop (it doesn’t matter what your OS is). Regain PST Splitter - Home Screen
  2. Then select and pick the desired PST file that you want to split.Select PST file for splitting
  3. As per your requirements, fill in the appropriate options in the software.Select Splitting options
  4. Choose the destination location where you want to save the split files.Select location of resultant PST file
  5. Lastly, to finish the procedure, press Next.

Furthermore, you can use this program to divide a corrupt PST file without losing any data. It can split a password-protected Outlook PST file into manageable chunks.


MS Outlook become a necessity of any business these days, it uses on a daily basis. As time has passed, the size of the mailbox increases gradually in MS Outlook. Higher size of the mailbox raises issues in the Outlook application like hanging, slow working, etc. To avoid these issues you can increase the size of PST file as we already described above in the blog or you can use Mailbox Cleanup and Compact option to reduce the mailbox size. You can also try professional tool to split large pst file into smaller pst files. It is up to you which you prefer.

Frequently Asked Questions

Ques1. What are the maximum sizes for PST files in Outlook?
Ans. There are probably no file size limits in Outlook; however, Microsoft suggests keeping PST file size below 2GB to save them from corruption.

Ques2. I want to create a PST file for each of my folders. Can I do it with your tool?
Ans. Yes, Regain PST splitter tool provides different filter options to split PST files. You can easily apply filters and create new PST files for each of your folders. Apart from this, there are several other filter options available in the tool.

Ques3. Can I recover the corrupt PST files with your tool before splitting them?
Ans. No Regain PST splitter tool only processes the healthy PST files. If you have corrupt PST files and want to split them, then we suggest using the Regain Outlook PST recovery tool. It will do both tasks for you.

Ques4. Can I use the Regain PST splitter tool for free?
Ans. Yes, we offer a free version of our tool so users can easily evaluate the software skills and compatibility. The Regain PST splitter tool also comes with a free version that allows users to process the first 30 items per folder without spending a penny.

Author: Henry Bray

Henry Bray is a young technologist and content a Content Writer at Regain Software, loves to write about MS Outlook, MS Exchange Server, Office 365, Mozilla Thunderbird and many more email applications.

Leave a Reply

Your email address will not be published. Required fields are marked *