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