Factory Reset an iPhone or iPad

A full erase returns the device to setup assistant state. It is the right step before selling or when troubleshooting severe software issues.

Checklist

Back up anything you need
Sign out of iCloud / turn off Find My (removes Activation Lock for the next user)
Settings → General → Transfer or Reset → Erase All Content and Settings

Stuck during erase?

Use Recovery mode and restore with a computer, then see error fixes.