How to Change from Legacy to Uefi boot Without Reinstalling Windows 10

How to Change from Legacy to Uefi boot Without Reinstalling Windows 10

1. Check BitLocker Status

Open Command Prompt (Run as Administrator) and run:

manage-bde -status

If BitLocker is Enabled, suspend it first:

manage-bde -protectors -disable C:

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2. Validate the Disk Before Conversion

Run the following command to validate your disk:

mbr2gpt /validate /allowFullOS

If successful, the result will look like this:

MBR2GPT: Attempting to validate disk 3
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
MBR2GPT: Validation completed successfully

If you see "Validation completed successfully", your disk is ready to be converted.

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3. Convert MBR to GPT

Run one of the following commands:

Automatic (commonly OS is installed on Disk 0):

mbr2gpt /convert /allowFullOS

Or specify the disk number manually:

mbr2gpt /convert /disk:0 /allowFullOS

Note: Replace 0 with your actual OS disk number if different.

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4. Rebuild UEFI Boot Files

After conversion completes, rebuild the UEFI boot files:

mountvol S: /s
bcdboot C:\Windows /s S: /f UEFI

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5. Restart and Configure BIOS to UEFI

Restart your computer and enter BIOS. Change the following settings:

• Set Boot Mode to UEFI
• Disable CSM / Legacy Mode
• Set Windows Boot Manager as the first boot priority
• Save and Exit

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6. Verify After Booting

Once back in Windows:

• Press Win + R, type msinfo32 → Confirm BIOS Mode = UEFI
• Open Disk Management → Confirm the OS disk shows GPT

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Done ✅

Your system is now running in UEFI mode with GPT partition style without reinstalling Windows.