How do I manually install macOS Big Sur?

Manually installing macOS Big Sur may be necessary if you want to do a clean install of the operating system, upgrade from an older version that is no longer supported by the macOS installer, or install Big Sur on unsupported Macs. The process involves creating a bootable USB installer drive, erasing and formatting the target drive, and using the installer to deploy the OS.

When is a manual install required?

A manual install of macOS Big Sur is required in the following scenarios:

  • Doing a clean install – This wipes the target drive completely and installs macOS from scratch.
  • Upgrading from an unsupported version – The macOS installer only allows upgrades from the last 2-3 versions. Older versions require a manual install.
  • Installing on unsupported Macs – Apple drops support for older Macs with each OS release. Manual install is needed to get Big Sur on these devices.
  • Resolving upgrade issues – A manual install may resolve problems faced when upgrading using the normal procedure.

If you do not face any of these situations, it is recommended to use the standard upgrade procedure by downloading from the App Store and following the onscreen instructions.

Requirements for manual install

Before beginning the manual install process, ensure your Mac meets the following requirements:

  • macOS Big Sur supported Mac – Check the full list of compatible Macs.
  • At least 20GB of available storage space.
  • Back up your files and data – The process will erase the target drive.
  • Stable internet connection for downloading software.
  • USB flash drive of at least 12GB capacity for the installer.
  • Time and patience – The whole process can take a few hours.

Additionally, it is recommended to have access to another operational Mac to create the bootable USB drive if the target Mac cannot be booted up normally. The install process will require rebooting from the USB drive.

Step 1 – Get macOS Big Sur installer

The full macOS Big Sur installer app needs to be downloaded from the App Store using one of these methods:

  • App Store on supported Mac – Open the App Store on a Mac already running Big Sur or later and find the Big Sur installer under Updates. Click Download.
  • finder on supported Mac – Alternatively, you can get the installer app by going to /Applications in Finder on a Big Sur or later Mac. Right click on ‘Install macOS Big Sur’ and select Show Package Contents. Find Contents > SharedSupport folder and copy InstallESDDMG.pkg to another location. This is the full installer file.
  • Apple Developer account – Sign in to with your Apple ID linked to a paid Apple Developer account. Go to More Downloads > Command Line Tools for Xcode 12.x and download the dmg. Mount it and run the installer inside to get access to macOS Big Sur full install app.
  • AppleSeed account – If you are registered with Apple’s AppleSeed program for testing pre-release software, the Big Sur installer can be downloaded from the AppleSeed Software Updates panel.

Once you have the installer ready, proceed to creating the bootable drive.

Step 2 – Create macOS Big Sur bootable installer drive

A bootable USB flash drive needs to be prepared with the macOS installer to facilitate the clean install process:

  1. Get a USB flash drive with minimum 12GB capacity and format it to Mac OS Extended (Journaled) file system using Disk Utility.
  2. Launch Terminal and enter the following command, replacing InstallESD.dmg with the path to your installer file:

    sudo /Applications/Install\ macOS\ Big\ --volume /Volumes/MyVolume

  3. This will convert the drive named MyVolume to be a bootable Big Sur installer drive. The process will erase all existing data on the drive.
  4. You can also use a utility like TransMac on Windows to format the drive and copy the installer files to make it bootable.

Once created, boot your Mac from this USB drive to begin the Big Sur install process.

Step 3 – Erase and format the target drive

As part of the clean install procedure, the target drive on which Big Sur is to be installed needs to be completely erased and reformatted:

  1. Reboot your Mac and immediately press and hold Command + R keys after you hear the startup chime to boot into Recovery mode.
  2. When the Recovery screen appears, go to Disk Utility from the top menu bar.
  3. Select the target drive on which Big Sur is to be installed from the sidebar.
  4. Click Erase at the top and set the following:
    • Name: Give the erased volume a name like Big Sur.
    • Format: APFS.
    • Scheme: GUID Partition Map.
  5. Click Erase to wipe and reformat the drive. This will delete all existing data.
  6. Exit Disk Utility once done and proceed with installation.

The drive is now ready for deploying a fresh copy of macOS Big Sur.

Step 4 – Install macOS Big Sur

With the bootable USB installer drive and erased target drive ready, we can now install Big Sur:

  1. Boot your Mac from the USB installer drive.
  2. On first boot, open Disk Utility from the menu bar and select the volume you erased earlier.
  3. Click Restore and select the USB drive as the source.
  4. Restore will deploy a copy of the installer files to the target drive.
  5. After completion, quit Disk Utility and proceed with installation.
  6. Follow the macOS installer prompts to complete the process. Be patient as this will take time.
  7. Your Mac will reboot a few times during installation. Make sure to boot from the target drive once that option appears.
  8. When done, you will be greeted with a fresh desktop. macOS Big Sur is now manually installed.

Some additional troubleshooting may be required if any errors occur during the process. Consult Apple’s support guides in such cases.

Step 5 – Complete post-install tasks

Upon completing the manual installation, follow these steps before restoring your files and apps:

  • Apply all available system updates for Big Sur via the Software Update preference pane.
  • Reinstall third-party apps like browsers, productivity suites and utilities.
  • Restore your files and data from backup.
  • Configure personal settings like wallpaper, Network settings and user accounts.
  • Verify that all your hardware, peripherals and accessories function correctly.

And that’s it! With these steps, you have manually installed the latest macOS Big Sur on your Mac. This will let you start from a clean slate. Be sure to maintain regular backups going forward.

Frequently Asked Questions

Q: Do I lose my data and apps when manually installing Big Sur?

A: Yes, the process completely erases the target drive, so you will lose all apps, files and settings. Be sure to backup important data beforehand.

Q: What Macs are compatible with Big Sur?

A: Big Sur supports Macs from late 2013 onwards, with exceptions. Refer to Apple’s spec list to confirm your model is supported.

Q: Why am I unable to get the Big Sur installer?

A: The installer can fail to download on unsupported Macs. Use a friend’s supported Mac or the Apple Developer method instead.

Q: Can I revert to an older OS after installing Big Sur?

A: Downgrading requires wiping the drive again and installing the older OS. You will lose current data and apps again.

Q: Is my Mac too old for Big Sur?

A: If your Mac is from before 2013, it most likely does not support Big Sur. Check Apple’s specs to confirm.


Manually installing macOS Big Sur requires creating a bootable USB installer, erasing and formatting the target drive, booting from the installer, and deploying the OS files. It allows you to perform a clean install, upgrade unsupported Macs, and resolve upgrade issues. Backup your data, obtain the full installer beforehand, and allot adequate time for the multi-step process. You will have to reinstall apps and restore data after. When in doubt, consult Apple’s support documentation for assistance.