How to quickly make a Mac OS X bootable USB on Windows

i Mac running OS X Yosemite

If you’re still using a Mac OS X the time will come when your computer won’t boot, or a problem may arise where you can’t take control of the device, and booting from an OS X installation media will be required.

This is why it’s recommended that you make a Mac OS X bootable USB when your Mac is in working conditions. However, if you find yourself on a scenario where your device (iMac, MacBook Pro, Air, Mac Pro or Mini) is not responding and you happen to have a Windows device, then you can still be able to make a USB bootable installation media for your Mac OS X to reinstall the operating system using the Recovery Assistant.

These instructions will also work for Windows users, who are running Mac OS X on a virtual machine and need to upgrade to the latest version. For instance, to OS X Yosemite.

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.
  • 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).

Now that you have all the necessary ingredients, you’re ready to make a Mac OS X bootable USB using the DMG file of the operating system with the steps below.

How to create Mac OS X bootable USB installation media

Before you can use TransMac, you may first need to partition your USB flash drive with a GPT partition, as a normal MBR partition may not work. To do this, you’ll need to use the Diskpart command-line utility on Windows.

Setting up GPT partition

Use these steps to set up a USB drive with a GPT partition:

  1. Open Start on Windows 10.

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

  3. Type the following command to open Diskpart and press Enter:

    diskpart
  4. Type the following command to determine the USB flash drive and press Enter:

    list disk
  5. Type the following command to select the storage and press Enter:

    select disk 1
    Quick tip: The select disk 1 command as an example, but you have to replace 1 with the number of the flash drive you want to use.
  6. Type the following commands to delete everything from the USB thumb drive and press Enter:

    clean
  7. Type the following command to convert the drive into a GPT partition and press Enter:

    convert GPT
  8. Type the following command to select the new partition and press Enter:

    create partition primary

    Creating a GPT partition to build a Mac OS X bootable drive on Windows 10
    Creating a GPT partition to build a Mac OS X bootable drive on Windows 10

After you complete the steps, the USB flash drive from MBR to GPT format, you can use the steps below to create a bootable USB installation media to install Mac OS X.

Creating USB install media

Use these steps to create a bootable media to install Mac OS X:

  1. Download and install a copy of TransMac.

    Quick note: TransMac is a paid software, but it has a 15-day trial solution, that give us more than enough time to move the DMG files to the USB drive from Windows. (If you want to support the developer, you can purchase the full version.)
  2. Insert the USB drive that you’ll use to fix your installation of OS X. (Remember that all the data in the USB will be erased. Make sure you take off any important documents.)

  3. Right-click the TransMac software icon and Run as administrator. (You’ll be prompted to Enter Key or Run, because we’ll be using it once, click the Run option.)

  4. On the left pane, you’ll see all the Windows PC drives listed, right-click the USB drive that you’re intending to use to reinstall Apple’s OS X and select the Restore with Disk Image option.

    TransMac Restore with Disk Image

  5. In the warning dialog box, click the Yes button.

    TransMac Warning

  6. Use the Restore Disk Image to Drive dialog box to browse for the DMG file with the installation files for Mac OS X Yosemite in this case, and click the OK button to create a bootable USB of the operating system.

    OS X to USB on Windows

    Now, you’ll have to wait a long time. No kidding. It could take one or two hours to complete the process depending on your computer and other variables.

    TransMac Mac OS X to USB

Once your bootable USB installation media is ready, remove it and insert it into your Mac, power it on, holding down the Option key, and select the USB you just created to reinstall Mac OS X.

If you’re having issues trying to create a bootable media, you can get a USB flash drive that comes with Mac OSX ready to install.

Update September 23, 2019: This guide has been revised to make sure it includes the latest changes.