How to Clean Install macOS Big Sur

You may want to clean install your macOS because it’s running slow or otherwise not performing in the way you would want it to. Another reason that many people do this is if they suspect their Mac is infected with a virus. In this guide, we’ll be showing you how to clean install with the latest version of macOS, Big Sur.

Before we get started, you need to note that there are actually two different ways of going about this process. The first is the traditional way, using a bootable copy of the macOS installer on a device such as a USB or another flash drive, which would entail formatting your Mac before installing from the drive. There is however an easier option, which will allow you to complete the entire operation over the internet via macOS Recovery.

How to Clean Install macOS Big Sur with a USB

You will need:

1. A bootable USB stick or device (15GB or larger)

2. Admin privileges for the Mac

3. To create a backup in case anything goes wrong during the process. You can either use Time Machine, if not worried about copying settings and preferences from the old system, or you can sync all of your documents to iCloud before beginning.

Step 1 – Format the External Drive

To format your USB/external drive simply do the following steps.

Insert the USB/external drive into your Mac
Go to Applications, then to Utilities
Open the Disk Utility
Click on the drive, then click Erase. Note: you will need to make sure the drive is name ‘Untitled’
Select macOS Extended (Journaled) as the format type
You should now see scheme options. Select GUID Partition Map
Click Erase
This will then set up the USB/external drive ready to be used for the rest of the process. It could take a while, so you may need to be patient
Click Done

Step 2 – Get The macOS Install File

This part is super easy. Follow this link to get Big Sur (free) on the Apple store.

Once you have clicked to download, you will get a warning message telling you that you already have the version of macOS installed. Simply click Continue.

After entering your Apple ID and password as prompted, the download will begin. Again, this could take a little while, as the download for Big Sur is 12.6GB, so a little patience is required. When the download finishes, you will be prompted to begin the install straight away. Do not do this! Instead, hit Command + Q to quit the installer and locate it in the application folder (or use Searchlight to locate).

Step 3 – Create a Bootable USB Disc

First, hit Command + Space Bar and look for Terminal.
If it’s not already connected, connect the USB now and make sure once again that the drive is called ‘Untitled’
Open Terminal then copy and paste the following:

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia –volume /Volumes/MyVolume (MyVolume being the name of your USB/external drive, which should be called Untitled)

Press Return, then enter your password, then press Return again
Terminal will now run through its process of erasing the drive and copying the installer file to it. Again, this is going to take a while.

Step 4 – Wipe your Mac

At this point in the process, you’re going to want to make sure that everything is backed up that you wish to keep.

When ready, do the following:

Connect the USB once more
Turn on, or reboot your Mac while holding down the option (alt) key. This should take you to the Startup Manager
Choose to install the macOS from the drive and click ‘Disk Utility’
Click your Mac’s startup disk (likely Macintosh HD or Home)
Click Erase. The startup disk will now format
Go back to Utilities, but this time select Install macOS
Choose the startup drive as the location to install
Once complete, you can then retrieve your files from backup, and/or redownload anything you want to have.