How to Find the Serial Number on your MacBook
Choose Apple () menu > About This Mac. The window that appears lists your computer’s model name—for example, MacBook (Retina, 12-inch, Early 2016)—and serial number. You can then use your serial number to check your service and support options or to find tech specs for your model.
Close your MacBook and turn it over. The serial number is on the underside of the computer, near the regulatory markings.