Changing the default *.pst and *.ost sizes

Last reviewed on August 8, 2013

Beginning with Outlook 2003, the new Unicode pst/ost format support up to 1TB file size. Since this is not practical for most people, Microsoft set a default of 20 GB (Outlook 2003 or 2007) and 50 GB for Outlook 2010. While this size is fine for most people, it can be raised (or lowered) if needed by setting two registry values.

Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST (replacing xx with your version of Outlook: 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.)

Unicode pst format

For Unicode pst and ost files, create DWORD values of

MaxLargeFileSize
WarnLargeFileSize

Add the DWORD to the RegistryEnter a decimal value in MB. For example, 100 GB = 102400 Decimal (a GB to MB or bytes converter is below). Maximum Unicode pst/ost file size is 1TB or 1024 GB.

For ANSI format pst file, you need to create DWORD values named

MaxFileSize
WarnFileSize

Enter a decimal value in Bytes. For example, 1 GB = 1073741824 Decimal (a MB or bytes converter is below). Note that the maximum file size for ANSI pst is 1.9 GB.

Edit the registry

Administrators can control it using group policy by editing the following key.

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\PST

As always, replace xx with your version of Outlook: 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.

MaxLargeFileSize – this value sets the maximum size of a Unicode pst or ost. In Outlook 2010, the default is 50 GB, in Outlook 2003 and 2007, its 20 GB. Value range (in Hex) is 0×00000001 – 0×00100000; when entering the value in Decimal, use MB.

WarnLargeFileSize – this value sets the warning level used with Unicode pst/ost files, so you know when the pst or ost is too large. In most cases, especially with smaller pst/ost files, 500 megabytes should be sufficient but I recommend warning at 2 – 5 GB under the max file size for large pst files or if you receive large attachments by email. When entering the value in Decimal, use MB.

ANSI pst format

MaxFileSize – this value sets the maximum file size for ANSI format pst files. The default is 1.933 GB (2075149312 bytes), with the maximum allowed value of 1.9375 GB (2080392192 bytes). Value range (in Hex) is 0x001F4400 – 0x7C004400. When entering the value in Decimal, use bytes.

WarnFileSize – this value set the warning limit for ANSI format pst files. The default is to warn when the pst reaches 1.816 GB (1950368768 bytes) Value range is 0×00042400 – 0x7C004400. When entering the value in Decimal, use bytes.

Enter the values under the appropriate key:

Outlook 2013: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST
Outlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST
Outlook 2007: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST
Outlook 2003: HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST

Administrators will set these values using group policy:

Outlook 2013: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\PST
Outlook 2010: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\PST
Outlook 2007: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\PST
Outlook 2003: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\PST

Restore Default Values

To revert to the defaults, if the pst is larger than the default size, shrink the pst or ost so that its well below 20 GB (Outlook 2003/2007) or 50 GB (Outlook 2010/2013) or below 1.8 GB for ANSI format, then delete the appropriate MAX* and WARN* registry keys for the pst format.

Restart Outlook for the changes to take effect.

Do it for me

If you don’t want to edit the registry yourself, you can use the following .reg files to add the Unicode values to the registry.

Outlook 2013
100GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

Outlook 2010
100GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

Outlook 2007
100GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

Outlook 2003
100GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

More Information

How to configure the size limit for both (.pst) and (.ost) files in Outlook 2010, Outlook 2007, and in Outlook 2003 (MSKB)

Written by

Diane Poremsky
A Microsoft Outlook Most Valuable Professional (MVP) since 1999, Diane is the author of several books, including Outlook 2013 Absolute Beginners Book. She also created video training CDs and online training classes for Microsoft Outlook. You can find her helping people online in Outlook Forums as well as in the Microsoft Answers and TechNet forums.

17 responses to “Changing the default *.pst and *.ost sizes”

  1. Paarass

    I have problem that my mail box data file size limit is not increasing from 1.8 gb, whereas my need is atleat 20 gb.
    i have read the MSKB article 2months ago and do as directed but in vain, also read many other articles on online blogs (as above) but still my mailbox stop send/receive at 1.8GB. and I have to delete some email, that i wish to keep.
    I will be grateful if anyone help me.
    recently after reading this article, I have deleted the MaxFileSize and WarnFileSize and only keep the MaxLargeFileSize and WarnLargeFileSize with values set for 50GB. but still after restarting the MS Outlook, its stuck on 1.8 gb limit.

    Waiting for some help from you people. thanks, Paarass (paaras@gmail.com)

  2. George

    I am using Outlook 2007. I have set up two emails/data files. The default is Exchange (ost), and the other is a Pop email account (pst). My pst email data keeps reverting to the ost default file without me doing anything, thus dumping all my personal emails into my exchange email inbox. Very annoying. any idea why this is happening?

  3. Mark Pavey

    Hi Diane - thanks for this very useful article. Unfortunately for me within the Registry Editor --> hkey_current_user --> software --> policies --> Microsoft i then only have 2 folders (SystemCertificates and Windows). There is no 'office' folder. Do you know why and what the fix is? Im on XP, and just installed MS Office 2010. Any help would be very greatly appreciated (i've got 180gb of email to transfer over from Outlook Express and it always crashes at 50GB due to this limit when i try to import!!).

  4. Mark Pavey

    Hi Diane - wow, thanks for very fast reply! Sorry i've never done any of this register editing before. If possible, could you tell me step-by-step how to run the '100 GB Key'? Do i need to install some program that handles the registry edits, such as 'Windows Registry Editor Version 5.00'? Basically, i have no idea where to put below!

    [HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST]
    "MaxLargeFileSize"=dword:00019000
    "WarnLargeFileSize"=dword:00017c00

  5. Mark Pavey

    Sorry i've never done any of this register editing before. If possible, could you tell me step-by-step how to run the '100 GB Key'? Do i need to install some program that handles the registry edits, such as 'Windows Registry Editor Version 5.00'? Basically, i have no idea where to put that key. PS. sorry for posting this a 2nd time, just realized i did not 'reply' to your posting so perhaps you were not notified.

  6. Hector Frohm

    Hello Diane,
    Thank you for your article. However, just like the other posts on limiting ost file size, it doesn't indicate what Outlook will do when the maximum file size is reached...
    When the PST size is not limited, but the OST file size is... What happens when the OST limit is reached ? I know Outlook will try to compact, but if the PST size is 20GB and the OST limit is set to 5GB.. will outlook decide to only cache the most recent 5GB worth of e-mails and make a call to the Exchange server if displaying an older e-mail is required ? Or will it just stop receiving new e-mails ?
    Thanks !!
    Hector

  7. Troy Gibson

    i just changed the registry key under one of my users in the office. we are on a domain and have an in-house exchange server running exchange 2010 sp2. the user that i changed the registry key is using office 2010 and when i go to file on the top left corner, the data file size is still 20 gigs. is there a reason why this is happening? it seems the register edit isn't working. he used to use 2003 in the beginning and has upgrade to 2007 and then 2010..

    thanks in advance

  8. Timothy

    Diane,

    I am using Office 2007 on a Windows 7 machine. I used your "do it for me" option to increase the file size to 100GB with a 95 GB warning. I am still getting the warning that my Outlook.pst has reached its maximum size. I checked the registry and the values have been set properly by your "do it for me" option. I have restarted my computer. Why am I still getting this warning?

  9. Timothy

    Sorry Diane, took me some time to figure out where to look for the pst file. I made a screen shot of the warning, the registry, and the file size:

    https://www.dropbox.com/s/l4bna9rhbvq8sm4/Screenshot%202014-02-20%2012.46.43.png

    Hopefully you can help!

  10. Timothy

    I created a new pst file called Outlook 2007 so I remember this is the larger one. Your next instructions are beyond my limited skill set :( Which is the easiest ways to move the data into the new pst file? Is there a reference (step by step kind of thing) you could recommend that I could use as a guide to help me do this move? If not, would you be able to provide some more specific instructions on how to do this move? I don't know what I would do if I lost my email data!

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