Check the passport biodata page
Look for the field labeled Passport No., Passport Number, or Passport #
The number is usually printed near the top of the identity page
It may be on the same page as your photo, name, date of birth, and nationality
Check previous passport copies or scans if you do not have the physical passport
Review visa application forms or travel records where you may have entered it
Contact your passport-issuing authority if you cannot find it
If your passport is lost or stolen, report it to the issuing authority immediately