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 on the barcode label for the serial number
Check the SIM tray on some older models
Connect the iPhone to a Mac or PC
Open Finder on Mac or iTunes on Windows or older Mac
Select the iPhone
View the serial number in the device summary
Check the Apple ID device list
Go to appleid.apple.com
Sign in
Select your iPhone to view its serial number
Check the back of some older iPhone models
Look near the bottom for the serial number