The nine-digit number on a U.S. passport is on the top right of the photo page just inside the cover of the passport. It's printed right under Passport No./No. du Passeport, No. de Pasaporte. If you don't have the passport with you, the number can be recovered from documents you fill out as part of international travel or from the wallet-size passport card that comes with a passport.
Check e-tickets for international travel to find the passport number, required when filling out purchase information and itinerary. Your hotel receipt may also have your passport number filled in — in a pinch, the front desk may be able to retrieve it for you if you gave it upon booking. Copies of arrival and customs documents from immigration processing at the airport contain your passport number.
If your passport is missing or misplaced, you can obtain a copy of your passport record by mailing a notarized request to the Department of State Passport Services in Washington, D.C. The loss or theft of a passport during overseas travel should be reported immediately to the U.S. embassy or consulate. Information about hours and locations is available from the State Department's toll-free number: 888-407-4747. New passports have new numbers.
To report a passport lost or stolen, call the Department of State. To replace a missing passport, make an appointment in person at a Passport Agency or Center. The new passport arrives in eight days or fewer. Once an owner reports a passport as lost or stolen, it is invalidated and cannot be used as identification or for travel purposes.
If your find your passport after reporting it lost, mail it to the address provided by the Passport Agency. You can choose to have the new passport cancelled and the old one returned; otherwise, the agency automatically destroys the old passport and sends you the new one.