By AOMEI / Last Updated November 29, 2019

Convert to GPT Disk Grayed Out in Windows Disk Management

As we’ve learnt before, the maximum size of an MBR style disk is limited to 2TBs and four primary partitions. A disk in the GPT style is able to hold up to 128 primary partitions and more than 16 million TBs of data! When compared with MBR, GPT disk have greater compatibility with modern hardware and systems as they use the newer UEFI boot mode. A user that wants to take full advantage of a disk that’s larger than 2TBs or needs more that 4 primary partitions will need to convert it from MBR to GPT. If you want to read more about the differences between MBR & GPT then click on the link.

Disk Management is a partition tool built-in to Windows that enables users to convert their MBR disks to GPT. However, most users who try to use Disk Management will find that when they right click the MBR disk the “Convert to GPT Disk” option is grayed out, as seen in the screenshot below.

Convert to GPT

There are two possible reasons why you can’t easily convert the disk to GPT. One is that there are existing partitions on the disk, and the other is that the selected disk contains system files. If you only want to use Windows Disk Management to convert the disk to GPT then you will need to backup all of the data on the disk and delete all the partitions. The “Convert to GPT” option will no longer be grayed out once the disk is empty.

Unfortunately, for the majority of users this is impossible as deleting all data includes uninstalling Windows which you can’t do if you want to use Windows built-in tools to convert the disk. The only way to avoid data loss from both of these methods if by backing up and then restoring your disk after the conversion. Depending on the size of your drive this may take a considerable amount of time and it can be prone to errors.

There are two better solutions for converting the disk to GPT:

  • Convert to GPT via CMD (better for data disks that don’t contain system partitions)

  • Convert to GPT without losing your data using AOMEI Partition Assistant Professional edition.

Step by step guide to Converting to GPT without Data Loss

AOMEI Partition Assistant Professional is reliable and powerful partition manager that can help you convert MBR to GPT without losing any data when you find yourself unable to use Window Disk Management. When compared with Disk Management, AOMEI Partition Assistant is far more powerful and able to complete a whole range of advanced disk management features such as directly converting to GPT/MBR, resize partitions, move partitions, merge partitions, make bootable devices, and more. AOMEI Partition is fully compatible with Windows 10, 8/8.1, 7, Vista, and XP.

Step 1. Install and launch AOMEI Partition Assistant. Right-click the disk you want to convert and select “Convert to GPT Disk”.

Convert Data Disk to GPT

Step 2. Click "OK" to confirm the operation.

OK to GPT Data Disk

Step 3. You can now preview the conversion. To apply the changes, please click "Apply" on the top left of the toolbar.

Apply to GPT Data Disk


Helpful Tips: If you encounter issues with converting to GPT when using Windows Server 2003, 2008, and 2018 then check out AOMEI Partition Assistant Server edition.

Convert to GPT via Command Prompt

Step 1. Click Start, type "cmd", and right click command prompt, and select "Run as Administrator". Or press "WIN+R", type "cmd" and press Enter to open command prompt. Then, enter "diskpart" in command prompt and press enter to run the built-in utility.

Step 2. Type "list volume" to find out if there are any partitions or volumes on the MBR disk. If there are, you need to use DiskPart delete partitions before continuing.

Helpful Tip: You can delete all of the volume and partitions by using the “CLEAN ALL” command. This will erase any data stored on the disk.

Step 3. Type "list disk", and press Enter. This will show you all the disks on your computer. Make note of the disk number that you want to convert to GPT. In this guide we will use disk 1 as an example.

Step4. Type "select disk 1", press Enter. Diskpart will remind you that the disk 1 is selected.

Step 5. Type "convert gpt", press Enter to submit the operation. After a short wait, you will find that command prompt says “DiskPart successfully converted the selected disk to GPT format”. The below screenshot outlines the entire process.

diskpart convert to gpt

Conlusion

The majority of Windows users will find themselves needing to convert from MBR to GPT, however, there may be the odd circumstance where you need to the do the reverse (GPT to MBR). Usually, this is because they are using Windows 2000, Windows 2003 32-bit, or Windows XP 32-bit as these operating systems don’t support GPT formatted disks. If you do use a GPT disk with these OS’s, then it will show up as a ‘GPT protective partition’ and you will be unable to access your data. Fortunately, AOMEI Partition Assistant is also able to help you convert GPT to MBR without losing any of your data.

Notes:

  • When converting a system disk between MBR and GPT styles, if you want to guarantee that the system will be bootable then you will need to enter the BIOS and change the boot mode after the conversion has finished. For more information on BIOS and EFI (UEFI), please refer to GPT formatted disk legacy boot not supported.

  • When converting between MBR and GPT disks on Laptops, please make sure that the battery will last longer than the conversion process, we recommend you plug your Laptop into a wall socket.

  • To protect your data, you mustn’t stop/terminate the process once it has begun.

  • If you find you are unable to convert a disk to GPT, then you should use AOMEI Partition Assistant Standard to convert between MBR and GPT on a data disk without losing data.