Changing the default *.pst and *.ost sizes

Last reviewed on November 11, 2014   —  37 comments

Beginning with Outlook 2003, the new Unicode pst/ost format support much larger data files, with the default data file size set to 20 GB (Outlook 2003 or 2007) and 50 GB for Outlook 2010 or 2013. While this size is more than enough for most people, it can be raised in Outlook 2003/2007, if needed, by setting two registry values. The default file size in Outlook 2010/2013 of 50GB is currently the maximum recommended limit for Outlook 2003 and up.

Note: At this time, the maximum recommended ost or pst file size is 50GB.

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


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


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.

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 and Outlook 2013, the default is 50 GB; in Outlook 2003 and 2007, it’s 20 GB. Value range (in Hex) is 0x00000001 – 0x0000C800; 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. The recommended warning is at 95% of the data file size. 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 0x00042400 – 0x7C004400. When entering the value in Decimal, use bytes.

Enter the values under the appropriate key for your version of Outlook:

Outlook 2013:

Outlook 2010:

Outlook 2007:

Outlook 2003:

Administrators will set these values using group policy:

Outlook 2013:

Outlook 2010:

Outlook 2007:

Outlook 2003:

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
30GB pst/ost – 29.5GB warning

Outlook 2010
30GB pst/ost – 29.5GB warning

Outlook 2007
50GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

Outlook 2003
50GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

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.

Please post long or more complicated questions at Outlookforums.

37 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 (

  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!


  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 !!

  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


    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:

    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!

  11. R. A. Mitchell

    I was able to upgrade my Outlook 2003 to 100 GB using the "Do it for me" link, it even created a PST registry key where none existed before (this was on a Windows 7 laptop). I tried to do the same on my new Windows 8 machine (also a laptop) but I had to create a PST key before anything happened. My question is why did I have to create that key and did this mess up my registry? Your response will be greatly appreciated.

  12. R.A. Mitchell

    Thanks for your prompt response. Yes, I was using the same Outlook 2003 program on my Windows 8 machine, it's also good to know there shouldn't be any problem. The other Outlook registry key entries were a bit different on the Windows 8 machine when compared to my Windows 7 laptop, don't know what that's all about but the new machine's Outlook program is not yet set up to link with my online accounts.

  13. R. A. Mitchell

    Thanks Diane;

    I'll keep looking into this and let you know if anything turns up. I doubt that it makes any difference, but both machines are ASUS brand notebook computers. I'll be linking the new machine to my online mail accounts soon and confirm that Outlook is behaving properly.

  14. George

    I am trying to enlarge my maximum file size for my outlook ost file but my windows 8 registry doesn't have the key HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook

    it only goes to HKEY_CURRENT_USER\Software\Policies\Microsoft

    surely there is some place that a max file size is kept, since outlook has told me I have exceeded it.

  15. gcsimpson

    I am using windows 8 and outlook 2013 installed from disk. All outlook activities are taking place in an OST account. Yesterday a popup said I had reached max file size. Tried to follow yours and microsoft's regedit suggestions,,, but I don't have the key


    only goes as high as


    and under that it only has SystemCertificates and Windows subkeys

    I suppose I could create the necessary subkeys but before I do, I'm wondering ...where is the registry key that is setting my current limit?

  16. gcsimpson


    I assume there is a generic setting in the registry for maximum file size and then when I create the key, I am overriding it for outlook files? could you direct me to the location in the registry where the generic maximum file size is currently set. Sorry for being so curious, but I like to have some minimum understanding of what I am doing and how it all works together.

  17. gcsimpson

    Thank you so much. I'll go to work on it.

  18. gcsimpson

    I feel like a do-do, but you say the above instructions are for PST and OST; however, everything seems to deal with PST,

    "Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST "

    I've even gone to the Microsoft site to save you the trouble of an answer but they have the same thing you have . . . only PST

    I could just use your macro, but I'm trying to learn, here. Do I change PST to OST or does PST set the values for both types of files.

    Ever thankful

  19. Fabio

    Thank you very much for your help, I'm a computer technician and was looking for this solution for a long time, it really helped me a lot.

  20. Felix

    Dear Diane,

    according to the Microsoft Knowledge Base the maximum valid setting for MaxLargeFileSize in Outlook 2010 and 2013 is 0x0000C800 - which translates to 51200 MBytes (50 GByte).

    However you offer .reg files that set this value to 100 GByte.

    Unless the information in the Microsoft Knowledge Base is wrong this setting should be ignored because it exceeds the Valid Data Range for MaxLargeFileSize.

    Can you (or maybe someone else) confirm that Outlook 2013 (or 2010) actually do support files significantly larger than 50 GByte?

    Kind Regards

  21. Jonathan Martinez

    how come the DO IT FOR ME is not working, i used to use it a lot and now is not available

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