Planning a clean install of macOS Sequoia on your Mac? Whether you’re troubleshooting, starting fresh, or just like keeping things tidy, this step-by-step guide walks you through the entire process — from downloading the full installer to creating a bootable USB and wiping your Mac.

📋 macOS Version History

To help you keep track of macOS releases:

macOS VersionRelease NameRelease Date
macOS 10.12SierraSeptember 20, 2016
macOS 10.13High SierraSeptember 25, 2017
macOS 10.14MojaveSeptember 24, 2018
macOS 10.15CatalinaOctober 7, 2019
macOS 11Big SurNovember 12, 2020
macOS 12MontereyOctober 25, 2021
macOS 13VenturaOctober 24, 2022
macOS 14SonomaSeptember 26, 2023
macOS 15SequoiaSeptember 16, 2024

Note: Release dates refer to official public releases, not beta or developer versions.

📦 DMG vs PKG — What’s the Difference?

Before downloading the installer, it’s helpful to understand two common macOS formats:

DMG (Disk Image)

  • Simulates a physical disk (like a CD or USB).
  • Doesn’t recognize file structures; it’s a raw bit-for-bit image.
  • When mounted, it appears as a virtual external drive.

PKG (Package)

  • Structured installation file with metadata.
  • Knows which files it contains and where they should go.
  • Executes an installer to copy files to their proper locations.

In this guide, we’re working with a PKG file, specifically InstallAssistant.pkg, which installs the full macOS Sequoia installer.

⬇️ Download the macOS Sequoia Full Installer

Head to Mr. Macintosh and download the latest full installer under:

macOS Sequoia PUBLIC Full Installer → InstallAssistant.pkg

  • This file is hosted on Apple’s servers and is the same version you’d get from the App Store.
  • It works for both Intel and Apple Silicon Macs.
  • After running the .pkg, you’ll find Install macOS Sequoia.app in your Applications folder.

💡 Note: The InstallAssistant.pkg method has been standard since macOS Big Sur. Earlier versions like Catalina or Mojave use a different approach.

💾 Prepare a USB Drive (32GB+)

Step 1: Choose a USB Stick

The full installer is ~17GB, so:

  • ❌ 16GB is too small.
  • ✅ Use a 32GB USB stick or larger.

Step 2: Convert MBR to GPT (If Needed)

macOS bootable drives must use the GUID Partition Table (GPT). To convert:

⚠️ Warning: This will erase all data on your USB drive.

  1. List Disks:
diskutil list
  1. Unmount the USB:
diskutil unmountDisk /dev/diskX
  1. Erase & Convert to GPT:
diskutil partitionDisk /dev/diskX GPT JHFS+ USB_Drive 100%
  • Replace diskX with your actual USB disk number.
  • GPT → Sets the partition scheme to GUID Partition Table.
  • JHFS+ → Formats the drive as Mac OS Extended (Journaled) (you can change it to ExFAT, APFS, etc.).
  • USB_Drive → The name of the drive.
  • 100% → Uses the entire disk for this partition.
  1. Verify Partition Scheme:
diskutil info /dev/diskX

Check that it says:

Partition Map: GPT

💽 Create a Bootable Installer

  1. Plug in your prepared USB stick.

  2. Open Disk Utility and format it as APFS, name it: macOS Sequoia installer.

  3. Run this Terminal command:

sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/macOS\ Sequoia\ installer
  1. Enter your password and wait for the process to complete. This may take several minutes.

🎉 Now you have a bootable macOS Sequoia USB installer!

📁 Backup Your Mac

Before wiping anything, back up your data. You can use:

  • Time Machine
  • A portable SSD (as you did!)
  • Or manually copy your ~/Documents, Downloads, Desktop, etc.

🧹 Erase Your Mac

Now you’re ready to wipe your startup disk. Follow the method based on your Mac type:

🔐 Apple Silicon or Intel Macs with T2 Chip

  1. Go to Apple Menu > System Settings
  2. Navigate to General > Transfer or Reset
  3. Click Erase All Content and Settings
  4. Follow the on-screen instructions

✅ Make sure only the USB boot disk appears at startup — this confirms your Mac is clean and ready.

💻 Intel-based Macs (No T2 Chip)

  1. Shut down the Mac.
  2. Hold Command (⌘) + R and press the power button to boot into Recovery Mode.
  3. Choose Disk Utility from the macOS Utilities menu.
  4. Select your startup disk and Erase it using the APFS format.

🛠️ Install macOS Sequoia

You’re now ready to install:

  1. Insert the USB installer.
  2. Reboot your Mac:
    • Apple Silicon: Hold power until startup options appear.
    • Intel: Hold Option (⌥) while powering on.
  3. Select the USB installer.
  4. Follow the on-screen instructions to install macOS Sequoia.

🔁 How to Reinstall Later

If you ever need to reinstall Sequoia again:

  • Boot from the USB installer you created.
  • Or enter Recovery Mode and choose Reinstall macOS Sequoia.

✅ Final Tips

  • Don’t skip the backup!
  • Make sure your USB drive is formatted correctly (GPT + APFS recommended).
  • If something goes wrong, try re-downloading the installer or using a different USB port.