Without a physical passport it can be difficult to obtain your passport number. Because this number is a security identification number, there is no way to obtain this information by contacting a passport agency or federal office. If you do not have your passport, you must apply for a replacement passport to obtain your information. When you get a passport, make a copy of the page containing your information in case it is lost.
Download the replacement passport application and complete. You can also get a passport application at your local post office. Gather your birth certificate, photo identification, passport-sized photos and fees.
Take the application to your local passport centre or post office. Submit your information and pay the applicable fees. Your new passport will be mailed to your home.
Read the number off copies in your records. Before travelling you should always make copies to keep at home and file with the U.S. Embassy in case your passport is lost or stolen. The number on these documents would be the same as your passport number.