How to Create a Bootable Windows 11 USB Drive on a Mac

There are numerous scenarios where you might need a bootable Windows 11 USB installer, such as building a new PC or diagnosing a corrupted system. If your only functional computer is an Apple Mac, creating this installer is notoriously difficult. Modern macOS versions no longer include the Boot Camp Assistant feature for creating Windows USB drives, and standard disk utilities often format the drives incorrectly for PC motherboards.

This guide explains the most reliable method for creating a bootable Windows 11 installation media on a Mac using the terminal and the free, open-source application Homebrew.

Requirements

• A Mac running macOS Catalina or newer.
• A USB flash drive with at least 8GB of storage space (all data on this drive will be destroyed).
• A stable internet connection.

Step 1: Download the Windows 11 ISO File

First, you must download the official disk image directly from Microsoft.

1. Navigate to the official Microsoft Windows 11 download page.
2. Scroll down to the Download Windows 11 Disk Image (ISO) for x64 devices section.
3. Select Windows 11 (multi-edition ISO) from the dropdown menu and click Download Now.
4. Select your preferred product language and click Confirm.
5. Click the 64-bit Download button. This file is larger than 5GB, so it may take some time depending on your connection.

Step 2: Install Homebrew and Wimlib

The primary challenge when creating a Windows 11 installer on a Mac is that the main installation file within the ISO (`install.wim`) is larger than 4GB. The FAT32 file system, which is required for maximum PC motherboard compatibility, cannot hold files larger than 4GB. We must split this file using a tool called wimlib, which we will install via Homebrew.

1. Open the Terminal application on your Mac (found in Applications > Utilities).
2. Install Homebrew by pasting the following command and pressing Enter:
   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
3. Follow the on-screen instructions. You will need to enter your Mac administrator password.
4. Once Homebrew is installed, install the wimlib package by typing:
   brew install wimlib

Step 3: Format the USB Drive

You must prepare the USB drive using the correct formatting standards.

1. Insert your USB flash drive into the Mac.
2. In the Terminal, type diskutil list and press Enter.
3. Identify your USB drive in the list (e.g., /dev/disk2). Be absolutely certain you identify the correct drive, or you risk erasing your Mac’s internal storage.
4. Format the drive using the following command (replace disk2 with your actual drive identifier):
   diskutil eraseDisk MS-DOS "WIN11" GPT /dev/disk2

Step 4: Copy Files and Split the WIM File

Finally, we will mount the downloaded ISO and copy its contents, splitting the problematic file in the process.

1. Locate the Windows 11 ISO file in your Downloads folder and double-click it to mount it. Take note of its mounted name (usually `CCCOMA_X64FRE_EN-US_DV9`).
2. Copy all files *except* the oversized `install.wim` file from the ISO to the USB drive using the Terminal. Run this command (adjusting the paths if necessary):
   rsync -vha --exclude=sources/install.wim /Volumes/CCCOMA_X64FRE_EN-US_DV9/ /Volumes/WIN11
3. Once the standard files have copied, use wimlib to split and copy the oversized file:
   wimlib-imagex split /Volumes/CCCOMA_X64FRE_EN-US_DV9/sources/install.wim /Volumes/WIN11/sources/install.swm 3800

The splitting process will take a significant amount of time. Once it completes and returns you to a new terminal prompt, eject the USB drive. You now have a functional, bootable Windows 11 installation drive ready to use on any standard PC.