A bootable USB installer is the most dependable way to install macOS on its own terms: a clean install when a Mac is sluggish or being handed to someone new, a rescue when a machine won’t boot, or setting up several Macs without re-downloading gigabytes each time. Built-in Recovery Mode covers most repairs, but a physical installer works even when the recovery partition is damaged, the Mac has no internet, or you need to erase and install from scratch. Here is the whole process.
What you need
- A USB flash drive, 16GB or larger (it gets fully erased — back up anything on it first).
- A working Mac to build the installer on, running macOS that supports the version you want.
- A stable internet connection to download the installer (roughly 12–15GB).
- About 30–45 minutes, most of it unattended.
Step 1: Download the full macOS installer
Open the App Store, search for the macOS version you want (for example “Sequoia” or “Sonoma”), and click Get. macOS opens Software Update and downloads the full installer app to your Applications folder — named something like Install macOS Sequoia.app.
When it finishes, an installer window usually opens automatically. Quit it (Command‑Q) without continuing — you only need the app on disk, not to run it. If you cannot find your target version in the App Store, Apple hosts direct links to older full installers in its support article “How to get old versions of macOS.”
Step 2: Plug in and identify the USB drive
Insert the USB drive. You do not need to format it first — the next command erases it — but you do need its exact volume name. Open Disk Utility (Applications → Utilities) and note the name shown in the sidebar, for example Untitled or MyUSB. The command below assumes the volume is named MyVolume; substitute your drive’s real name.
Step 3: Run the createinstallmedia command
Open Terminal (Applications → Utilities). The command comes bundled inside the installer app. For macOS Sequoia on a drive named MyVolume, it looks like this:
sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolumeSwap in your macOS version and volume name. Press Return, type your admin password (it stays invisible as you type), and press Return again. Type Y to confirm the erase. Terminal will show “Erasing disk…” then “Copying to disk…” and finally “Install media now available at /Volumes/Install macOS Sequoia”. That last line means it worked. The drive is now renamed to match the installer — that is normal.
If you get “command not found” or a path error: the installer name or macOS version in the path is wrong. Drag the installer app from Finder into Terminal to paste its exact path, then add /Contents/Resources/createinstallmedia --volume /Volumes/MyVolume after it.
Step 4: Boot from the USB installer
How you pick the boot drive depends on your Mac’s chip. Not sure which you have? See our recovery guide, which explains the two startup paths.
Apple silicon (M1, M2, M3, M4)
Shut the Mac down fully. Press and hold the power button until you see “Loading startup options.” Release it, click your USB installer (it appears alongside your internal disk), then click Continue.
Intel Macs
Shut down, then power on while holding the Option (⌥) key until the Startup Manager appears. Select the orange Install macOS volume with the arrow keys or mouse and press Return.
If the installer will not show up, make sure the drive is in a port directly on the Mac (not through a hub or dongle), and on Apple silicon confirm you are using Startup Options, not the Option key — the Option key is an Intel‑only shortcut.
Step 5: Install or clean-install macOS
Once booted, you land in the macOS Utilities window. To install over your existing setup (keeping files), choose Install macOS and pick your internal drive. For a true clean install, first open Disk Utility, select your internal drive, click Erase (format APFS), quit Disk Utility, then choose Install macOS. Planning to sell or hand off the Mac? Follow our factory-reset guide so Activation Lock and your Apple account are cleared correctly first.
Frequently asked questions
How big does the USB drive need to be?
16GB is the practical minimum for modern macOS installers; 32GB gives comfortable headroom. The drive is fully erased, so use a spare.
Can I make the installer on a Windows PC?
Not with createinstallmedia — that command only runs on macOS. You need access to a Mac to build a supported, reliable installer. If you don’t have one, Recovery Mode’s internet reinstall is your path instead.
Will this erase my Mac?
Making the USB installer only erases the USB drive. Your Mac is untouched until you actively choose to erase or install in Step 5.
Which macOS version should I put on it?
Use the newest version your Mac supports for security and app compatibility. If a Mac is too old for the latest release, download the highest version it officially supports from Apple’s older-installer list.
My Mac still won’t boot or install — now what?
If a clean install fails or the Mac won’t start even from USB, the issue may be hardware (storage, logic board). We buy and repair Macs in any condition — get a quick trade-in quote, or if you’d rather just upgrade, our Apple clearance deals start at $450.
Restoring a Mac to move on from it? Browse verified, ready-to-use Macs on clearance — every one is tested, reset, and covered by our own warranty.