How to Convert MBR to GPT Without Losing Data

Convert your Windows drive from MBR to GPT with Microsoft’s own tool, then switch to UEFI. No reinstall, no lost files.

Mohammad Shojib Ahmed

Oct 2026

2 min read

In short

Use Windows’ own MBR2GPT tool, then switch your BIOS to UEFI. No reinstall, no lost files.

▶ Prefer video? Watch this tutorial on YouTube

If you turned on Secure Boot for Windows 11 and your PC keeps going back to the BIOS instead of starting Windows, your system drive is almost certainly using the old MBR partition style. Secure Boot needs UEFI, and UEFI needs a GPT drive. Here is how I converted my drive from MBR to GPT with Windows’ own MBR2GPT tool, without losing a single file. I have used this on three PCs.

Tip: Back up anything important first. MBR2GPT is built into Windows and safe, but it changes how your drive starts up, so a backup is cheap insurance.

What you need

Windows 10 (version 1703 or newer) or Windows 11
An administrator account
Access to your BIOS

Step 1: Check that your drive is MBR

Right-click Start and open Disk Management.
Right-click the disk Windows is on (usually Disk 0, not a partition) and choose Properties.
Open the Volumes tab. If Partition style says Master Boot Record (MBR), carry on.

Step 2: Convert the drive to GPT

Search for cmd, right-click Command Prompt and choose Run as administrator.
Check the disk first: type mbr2gpt /validate /allowFullOS and press Enter. If you see “Validation completed successfully”, you are good to go.
Run the conversion: mbr2gpt /convert /allowFullOS
Wait a minute or two. When you see “Conversion completed successfully”, the drive is GPT and your files are untouched.

Windows will warn you that the firmware has to be switched to UEFI before the PC can boot properly. Do the next step before you try to start Windows again.

Step 3: Switch your BIOS to UEFI

Restart and keep pressing Delete (F2 on some boards) to open the BIOS. Menu names vary by brand. On my board it looked like this:

Open Boot, then CSM (Compatibility Support Module).
Set Boot Device Control to UEFI Only.
Set Boot from Storage Devices to UEFI driver first. This one matters most: if storage is not on UEFI, Windows will not start.
Leave Boot from Network Devices and PCI-E Expansion Devices on Legacy only.
Press F10 to save and restart.

Windows should now start normally, and Disk Management will show GUID Partition Table (GPT). You can now turn on Secure Boot.

If you get a blue screen

It usually means the PC cannot find the drive to boot from yet. Turn the PC off for a few minutes, go back into the BIOS, choose Load defaults, restart, then set UEFI mode again as above. Your files are still there. It is a boot setting, not a lost drive.