How to Install macOS from USB: Complete step-by-step guide

Knowing how to install macOS from a USB is one of those quiet superpowers I believe every Mac user should have. 

Whatever the reason, creating a bootable macOS installer gives you the flexibility to install any macOS version on any Mac. But since it’s a technical process, you’ll need to prepare well to avoid installation errors and data loss. 

In this guide, I’ll take you through how to install macOS from a USB, step-by-step, create a bootable installer, prepare the Mac, and see how to go about the installation safely.

Want to quickly check your Mac? Use this Mac Serial Number Lookup tool to easily find important details before installing macOS.

Preparing your USB installer

The first thing you need to do is check the size of your USB storage. Most older operating systems work well with 16GB USB drives, but you may need a 32GB drive for the more recent macOS versions. Updated versions of Tahoe, Sequoia, and Sonoma usually range from 20GB to 45GB, so 40GB drives are safer.

From there, you can format the drive to prepare it for macOS installation. To do this:

1. Open Disk Utility (Applications > Utilities).
2. Click on the USB drive.
3. Click Erase.
4. Choose format as APFS (plain) — the default format macOS expects for bootable installers.
5. Name it MyVolume.
6. Click Erase.

For Catalina or older,  use Mac OS Extended (Journaled) (GUID Partition Map).

Here's a handy guide for all macOS versions so you can learn more before you get started.

Download macOS installer

After that, download the macOS installer for the version you want. You have three options here:

• Download macOS installer via App Store: Simply search on App Store and click Get. This method works for macOS versions from High Sierra to the recent versions.

• Use Safari to download the macOS installer: From Sierra to Lion, use Safari and click on the specific version on the Apple website.
• Download the installer using Terminal: Use the command softwareupdate --fetch-full-installer --full-installer-version <number> where <number> is the macOS version (e.g., 26.0.1 for Tahoe). This method allows you to download specific updates, and you can use the command softwareupdate --list-full-installers to get a list of all versions available for your Mac.

Ensure you don’t choose a version that’s older than the one that came with your Mac, as it may not have the required drivers. After that, take a moment to go through your data, whether you want to clean up everything or just upgrade. 

Creating the Bootable macOS USB

This is the part that tends to feel a bit geeky, but it’s not hard. Here’s how to create a bootable Mac installer:

1. Open Terminal (Applications > Utilities).
2. Run the createinstallmedia command: sudo /Applications/Install\ macOS\ [version].app/Contents/Resources/createinstallmedia --volume /Volumes/[Name]. Replace “[version]” with the name of your macOS version (e.g., Tahoe) and [Name] with “MyVolume” or the name you used for your USB drive. If your macOS version has more than one word, like Big Sur, the format changes to Big\ Sur.app.
3. Enter your password when prompted and press Return.
4. Type Y to confirm erasure.
5. Eject the USB safely after all files have been copied.

When the files start copying after entering your password, be patient and let the process complete. Interrupting it will take you back to the first step, and it can even corrupt the USB drive.

Installing macOS from the Bootable USB

It’s now time to put your new installer to work. Note that the procedure varies depending on whether you are using an Intel-based Mac or a newer Apple silicon Mac.

Here’s how to install macOS from a USB:

1. Shut down your Mac (Apple menu > Shut Down).
2. Connect your macOS bootable USB:

• On Intel-based Macs: Press the power button, then immediately press and hold the Option (Alt) key.
• On Apple Silicon: Press and hold the power button until you see Loading startup options.

3. Choose the macOS bootable USB using the arrow keys (Intel) or the pointer (Apple silicon) and press Return.

4. Choose your language if prompted.

5. Option 1: Click Install macOS and choose your internal drive (usually Macintosh HD) to keep your files and settings. Option 2: Click Disk Utility to erase the startup disk. Go back and select Install macOS and choose the internal drive.

6. Follow the onscreen instructions.

Here’s how to erase your startup disk after selecting your USB:

1. Click Disk Utility.
2. Click on your internal drive.
3. Click Erase and choose APFS (for macOS 10.13 or later) or Mac OS Extended (Journaled) (for older systems).
4. Confirm, then close Disk Utility.
5. Go back and click Install macOS, choose your internal drive (usually Macintosh HD), and follow the on-screen instructions.

If you are using a Mac with the Apple T2 Security Chip and you find that you can’t select the bootable installer, enable external booting from the Startup Security Utility.

Troubleshooting common issues during USB installation

Even when you’ve seemingly done everything right, a few bumps can appear along the way. Here are the common issues you may face and how to get back on track:

• USB installer not recognized: Ensure that the USB is plugged in correctly and in the correct format. You can try a new port and another computer to see if the device is recognized.
• Installer doesn’t show at startup: Confirm that the USB drive is in the Mac OS Extended (Journaled) for older macOS, or ASPF for new macOS versions.
• Can’t install error: Check the time settings and set it to automatic.
• Repeated disk or installation errors: Run First Aid on the target drive from the macOS Utilities window. This will help correct any issues that can block installation.

Remember that getting the variables right in the createinstallmedia command in Terminal is crucial to ensuring that everything goes smoothly.

Why use a bootable USB installer?

A bootable macOS installer isn’t something you’ll need every day, but when you do, you’ll really appreciate having it: 

• Apple’s official installation method requires an active internet connection, and it fails when the connection goes down. 
• Creating a bootable installer provides reliability, and you can use it on multiple Macs without needing to download the installer again.
• A macOS bootable USB also allows you to reinstall older macOS versions, troubleshoot Macs that won’t run properly, and perform clean installs when your operating system feels clunky.

Due to the usability, I always ensure I have a bootable USB lying around for both emergencies and testing purposes.

Install macOS from USB: Done right

If you’ve followed all the steps correctly, you should now have a reliable macOS installer. You can use it to install older or incompatible macOS versions, do upgrades, and fix Macs that are slow or refuse to boot. It’s one of those small things that can save you from frustration.

If you are not doing a clean install, remember to clean up your junk with CleanMyMac to ensure your new operating system works as expected. You should also back up your important files with a tool like Get Backup Pro or Chronosync Express to avoid frustration. In case of any file loss, iBoysoft Data Recovery will help bring your files back even when the drive is unreadable or the Mac won’t boot.

All these apps are available on Setapp, and you can try them through Setapp’s 7-day free trial (alongside 250+ other apps). 

FAQ: Install macOS from USB

How do I create a macOS bootable USB?

You can create a macOS bootable USB by: 

• Downloading macOS: Get the macOS installer from the App Store or Apple’s official sources for the version you need.
• Formatting the USB drive: Use Disk Utility to erase and format the USB, ensuring the drive is properly prepared for macOS installation.
• Using the createinstallmedia Terminal command: Run the correct createinstallmedia command from the Terminal, specifying the exact macOS installer name and USB volume name. This command erases the USB and copies the installer files to make it bootable.

Can I install macOS from a USB on any Mac?

You can install macOS from a USB on almost any Mac. If the macOS version is the same as or later than the one your Mac shipped with, it should work. If it’s not supported, you’ll need to patch it with OpenCore Legacy Patcher (OCLP). However, avoid installing operating systems that are older than your Mac, as they won’t install or run correctly due to a lack of drivers.

Do I need to erase my Mac to install from a USB?

No, you don’t need to erase your Mac to install macOS from a USB, although it depends on what you want to do. If you just want to reinstall macOS to change versions while keeping your files, settings, and apps, you can skip erasing the drive entirely. But if your Mac has accumulated a lot of clutter or you are troubleshooting persistent issues, you can clean it. If you don’t want to erase the drive, use CleanMyMac to ensure the new macOS runs smoothly.

How long does installing macOS from a USB take?

The time taken to install macOS from a USB varies depending on your Mac model, the USB drive speed, and the macOS version, but it generally takes between 20 and 60 minutes.

What should I do if my Mac doesn’t recognize the USB installer?

If Mac doesn’t recognize the USB installer, start by checking whether the drive is plugged in correctly and try another port. If it still doesn’t appear, you should confirm that the disk is in the correct format and reformat it if necessary. If you can’t make it work, you can recreate the bootable USB drive, which will likely resolve the issues.

Can I use a bootable USB to downgrade macOS?

Yes, you can use a bootable USB to downgrade macOS if your Mac supports the older version you want to install. Note that downgrading is a bit trickier as you need to clean up the disk to avoid conflicts, so ensure you’ve backed up your files with a tool like Get Backup Pro or Chronosync Express.