This example shows macOS Catalina version 10.15 build 19A583.Īfter you’ve done this, you’re going to want to click the get button to download the latest version of Mac OS Mojave if you haven’t already. If you need to know the build number as well, click the version number to see it. You should see the macOS name, such as macOS Mojave, followed by its version number. From the Apple menu  in the corner of your screen, choose About This Mac.