Open the Settings app
Tap General
Tap About
Find Serial Number
Press and hold the serial number to copy it
Check the original iPhone box
Look for the serial number on the barcode label
Check the SIM tray on some iPhone models
Remove the SIM tray and look for the serial number
Connect the iPhone to a Mac or PC
Open Finder on Mac or iTunes on Windows or older macOS
Select the iPhone
Find the serial number in the device summary
Sign in to your Apple ID account
Go to the Devices section
Select your iPhone
View the serial number
Check the back of older iPhone models
Look for the serial number printed on the rear casing