Double click on your USB that contains the macOS installer or highlight it and press the return key.

Aside from using the built-in Startup Manager, you can also boot into Verbose, Safe, and Target Disk modes.

In addition to this, macOS users also have an option of picking a disk to boot the operating system from.

How Big Does A Usb Need To Be For Osx Mac For Creating

Otherwise you should have another Mac for creating a bootable USB.

Also the process needs to sufficient storage space on your USB.

So ensure to have at least 32GB or greater storage space on your USB drive.

In other words, if your Mac is not older than 2005, you should be fine.

Press Command Spacebar to access Spotlight, then type Disk Utility.

In our example, we have FAT32 file system which is compatible on Windows.

You need to erase and format the USB to be compatible with your Mac.

In most cases, your Mac will show the supported format by default and you dont need to change it.

On older Mac, you will see an additional scheme option, choose GUID Partition Map.

Open App Store on your Mac and search for the latest macOS version.

Remember, App Store will only have the latest version which is macOS Mojave at this point when we write this article.

Simply quit the installer without starting the installation.

Also make sure the downloaded macOS installer file is in Applications folder.

Press Command Spacebar and search for terminal to open Terminal app.

Terminal will ask you to confirm erasing the volume, press Y and hit enter to confirm.

After successful completion of the process, name of the USB drive will be changed similar to the installer file name like Install macOS Mojave.

When your Mac restarts, press and hold the Option key till Startup Manager opens.

The Startup Manager scans and lists the drives that are connected and bootable.

Note that the Startup Manager will only list volumes that include bootable volumes.

If you only see Macintosh HD like below then the USB drive is not connected to your Mac or not created properly with the installer file.

Remember, you need to have an internet connection for installing from USB as the installer needs to get updates for your Mac from Apples server.