macOS bootable USB using Windows
Rescuing a Mac using Windows

How to quickly create a macOS bootable USB on Windows 10

Here are the steps to create a macOS Catalina bootable USB media with GPT partition support on Windows 10 to rescue your Mac computer.

It doesn’t matter whether you use macOS or Windows 10, it’s just a matter of time until your device will refuse to start, which could happen for many reasons, including (and not limited to) file corruption, hardware failure, and buggy update. If the unexpected happens with an Apple computer, you can use a macOS bootable USB with the installation media to repair it.

This is one of the main reasons why you should always consider making a macOS bootable USB when your device is working properly. However, if it happens that none of your devices (MacBook, MacBook Air, MacBook Pro, iMac, Mac Pro or Mac Mini) aren’t working when you need them the most, then you can use a PC to rescue your Apple device. You can use a Windows 10, Windows 8.1, or Windows 7 device to quickly create a USB bootable installation media to reinstall macOS Catalina on your Mac.

In this guide, you’ll learn the steps to create a macOS Catalina bootable USB installation on Windows 10, which you can use to reinstall or upgrade the Apple OS.

Things to know before proceeding

Before you dive into this guide, you’ll need a few things:

  • A broken Mac computer with Mac OS X or macOS (version 10.12 or later).
  • A trial copy of the TransMac software.
  • One high quality USB flash drive with 16GB of storage.
  • A copy of Apple’s macOS (DMG file).

How to make a macOS bootable USB installation media

To create a bootable USB drive with macOS, use these steps:

  1. Download and install TransMac on your Windows PC.

    Quick note: This is a paid software, but it gives you a 15-day trial, which is more than enough time. (If this works for you and want to support the developer, you can purchase the full version.)
  2. Connect the USB flash drive you want to use to fix your Mac. (If you have any data on the USB, remember to make a backup, as everything on it will be erased.)

  3. Right-click TransMac, and select the Run as administrator option.

  4. If you’re using the trial version, wait 15 seconds, and click the Run button.

    Run TransMac on Windows

  5. On the left, right-click the USB flash drive, select the Format Disk for Mac option.

    Format Disk for Mac using GPT partition

    Quick note: You want to do this before creating the bootable media because there is a good chance that the drive was formatted using a Windows device. If this is the case, chances are that it’s using a MBR partition, and the USB drive needs a GPT partition to work on a Mac.
  6. On the warning message, click the Yes button to format the drive.

    TransMac format warning

  7. Enter a name for the drive, such as “macOS bootable USB” and click the OK button.

    Format USB for macOS with label

  8. Click the Yes button.

    TransMac overwrite warning

  9. If the formatting completed successfully, click the OK button.

  10. Right-click the USB flash drive, and select the Restore with Disk Image option.

    TransMac Restore with Disk Image option

  11. On the warning message, click the Yes button to confirm the data on the USB drive will be erased.

    TransMac delete warning

  12. Click the browse button on the right, locate the .dmg file with the macOS installation files.

    Selecting dmg macOS file to create bootable USB drive

  13. Click the Open button.

  14. Click the OK button.

  15. Click the Yes button.

    TransMac create macOS USB bootable drive warning TransMac creating macOS bootable USB installation media on Windows

Once you complete the steps, you can now insert the USB flash drive on your Mac computer to install, reinstall, or upgrade the operating system to the latest version of macOS, which can be Sierra, Catalina, or later.

How to create a GPT partition on a USB flash drive

If the USB flash drive is not working using TransMac, it could be still a partition problem. In this case, you want to redo the entire process again, but this time use the following steps to use the Diskpart command-line utility on Windows to create the appropriate GPT partition.

To create a GPT partition on a removable drive, use these steps:

  1. Open Start.

  2. Search for Command Prompt, right-click the top result and select the Run as an administrator option.

  3. Type the diskpart command and press Enter.

  4. Enter the list disk command to view all drives connected to your computer and press Enter.

  5. Type the select disk command followed the number assigned for the USB flash drive (e.g., select disk 4), and press Enter.

  6. Enter the clean command and press Enter.

  7. Type the convert GPT command and press Enter.

  8. Enter the create partition primary command and press Enter to complete the process.

Once you formatted the USB flash drive to a GPT partition, you can use the instructions mentioned above to use TransMac to create a bootable media, but this time skip the steps 5 through 9, and continue on step 10.

After the process completes, which can take up to an hour, connect the USB flash drive and power on your Mac holding down the Option key, select the USB drive to begin the installation of macOS.

If you’re having problems creating the bootable media, you can get a USB flash drive that comes with macOS Sierra on it with the link mentioned below. (I personally haven’t tried it, but it’s worth the try if nothing works.)