How to Make a Bootable macOS Sierra USB Install Drive If you want to do a clean install of macOS Sierra, or you have multiple Macs to install it on, then a bootable flash drive for is your best bet for easy installation. Here’s how to make one. The Easy Option: Disk Creator The easiest way to create a USB flash installer is with the free program, Disk Creator. Download the macOS Sierra installer and Disk Creator. Insert an 8GB (or larger) flash drive. If you have any other data on that flash drive, back it up now, because the installer will delete everything on it. Open Disc Creator and click the “Select the OS X Installer” button. Find the Sierra installer file. This is should be located in your Applications folder. Select your flash drive from the drop-down menu. Click “Create Installer.” When it’s done, insert your USB drive into any Mac, then launch the installer by holding down the Option key when you boot up your computer.