How to Convert MBR to GPT Disk Without Data Loss on Windows | Change Legacy to UEFI Boot Mode | Using MBR2GPT Tool

Many a time, during a Windows installation process, you get errors along the lines of “Windows cannot be installed to this disk. The selected disk has an MBR partition table.” It mostly happens when you try to install the latest version of Windows on your old computer that has an older MBR partition style. Windows now support the newer GPT (GUID Partition Table). In fact, the newly-released Windows 11 only supports the GPT partition style.
So, in this blog, I am going to show you, "How to Convert MBR to GPT Disk Without Data Loss on Windows", or "How to Change Legacy to UEFI Boot Mode Without Data Loss on Windows".

Change Legacy to UEFI without data loss on Windows

This guide is to strictly convert MBR to GPT without any data loss. You no longer have to use Diskpart and erase the whole hard disk to convert the partition table. We will be using an official tool from Microsoft called MBR2GPT for this tutorial.
MBR2GPT tool converts a disk from the MBR to the GPT partition style without modifying or deleting data on the disk.

Check Disk partition style

Before modifying your system configuration, I recommend checking the current settings to see if the system is set to MBR or GPT. To check Disk Partition Style:
  1. Press the Start menu key, search "disk management", and open the top result.
  2. On "Disk Management", right-click on the first disk (usually Disk 0) and select Properties.
  3. On the Properties window, switch to the volumes tab.
  4. Under the "Partition style" field, if the field reads "GUID Partition Table (GPT)", then the disk drive doesn't need conversion, but if you see the "Master Boot Record (MBR)" label, you can use the conversion tool to switch.
Once you complete these steps, you'll know if it's necessary to change the partition style on your device.
Also, if you need to change the partition, make sure that your computer meets the requirements of the MBR2GPT tool.

Requirements for MBR2GPT Tool

  1. Your PC must support UEFI. If you have an older computer and the BIOS only supports Legacy mode, you can’t utilize this method.
  2. All Bitlocker-encrypted volumes must be suspended for the conversion to take place.
  3. There are at most 3 primary partitions in the MBR partition table.
    To check the number of partitions, open "Disk Management". And, count partitions (boxes) left to first Disk (usually Disk 0). If there are more than 3 partitions, then you will need to merge all the partitions except the first and second partitions.
If any of these checks fails, the conversion will not proceed and an error will be returned.

Please NOTE:

  • If your computer running on Windows 10 Creator Update (Version 1707) or later, then it already has Microsoft’s MBR2GPT tool on your system. So, we can use this tool to Convert MBR to GPT Disk.
    To check the Windows version, use shortcut Windows key + R to open the Run dialogue, type winver, and press Enter key. On the "About Windows", you can find the Windows version.
  • And, if the computer running on Windows 10 Anniversary Update (Version 1607) or earlier (like Windows 7), then first upgrade your PC to the latest version of Windows 10.
    Here's the ultimate guide: How to upgrade your PC to Windows 10 for FREE?

Convert MBR to GPT Disk using MBR2GPT

  1. Open Administrator: Command Prompt.
    Press the Start menu key, type cmd, and then right-click on Command Prompt from results and select Run as administrator option. On UAC, click on the Yes button.
  2. Run validation command.
    On CMD, type mbr2gpt /validate /disk:0 /allowFullOS and press Enter key. Here, my disk number is 0. If it is something else for you, then change the disk number accordingly. This command is to validate all the configurations.
  3. If you get the “Validation completed successfully” message, you can proceed ahead.
  4. Run the conversation command.
    Now type mbr2gpt /convert /disk:0 /allowFullOS and press Enter key. Repeating again, make sure to change the disk number if you are doing this process for a different disk number.
  5. If you get a success message, well, congratulations. You have successfully converted MBR to GPT partition style and without any data loss. But wait, there is one more step to perform.

Change Boot Mode from Legacy to UEFI

Once you have converted the drive using a GPT partition style, your device will no longer boot correctly, until you change Boot Mode from Legacy to UEFI.
Method to change Boot Mode is different in different computer brands.
NOTE: Here, I am using HP Laptop
  1. Now, turn off the computer.
  2. Press the power button to turn on the computer, and then immediately press the F10 key repeatedly until the "BIOS Setup" opens.
  3. On "BIOS Setup", use the right arrow key to choose the "System Configuration" menu, use the down arrow key to select "Boot Options", then press Enter key.
  4. Use the down arrow key to select Legacy Support and press Enter key, select Disabled and press Enter key.
  5. Now, press the F10 key and select Ok to save and exit the BIOS Setup.
  6. After this, the computer will restart. And then the computer starts correctly.

Verify Partition Type and BIOS Mode

To verify that the computer is using a GPT partition style:
  1. Again open the "Disk Management" tool > Properties of first Disk > Volumes tab.
  2. And look for the “Partition style”.
  3. It should be showing “GUID Partition Table (GPT)”
The last thing left to do is to check if the device is using the UEFI Boot Mode.
You can use the "System Information" tool to check BIOS Mode.
To verify that your computer is using the UEFI Boot mode:
  1. Press the Start menu key, search for "System Information" and then open the top result.
  2. Under “System Summary”, look for “BIOS Mode“.
  3. If the System Information shows UEFI, then you have successfully changed Boot Mode to UEFI.
And that’s how you can "Convert MBR to GPT Disk Without Data Loss on Windows" or "Change Legacy to UEFI Boot Mode Without Data Loss on Windows".
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