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US Passport Number

General

United States Passport Book/Card Number

The unique identifier printed on a US passport, historically 9 digits and now issued in a 9-character alphanumeric format, used for identity and travel verification.

Definition

A US passport number is the unique identifier printed on a United States passport book or passport card, issued by the US Department of State to identify that specific travel document. It is used for identity verification at border crossings, visa applications, and international travel bookings, and — unlike a Social Security Number — changes every time the passport is renewed or replaced.

Historically, US passport book numbers were 9 digits, similar in length to an SSN, but the State Department has since introduced formats that mix letters and digits across different issuance batches and document types (books versus cards).

Formula

A US passport number has no publicly documented checksum digit. Format validation is limited to structural rules:

  1. Legacy format: 9 numeric digits, issued primarily before recent format updates.
  2. Current formats: a mix of alphanumeric characters, with length and allowed character sets varying by document type (passport book vs. passport card) and issuance period.

Because there is no mathematical check digit, format validation only confirms plausibility — actual document validity must be confirmed by the US Department of State or by machine-readable-zone (MRZ) verification at a border checkpoint, which combines the passport number with other document fields.

Worked Example

A structurally plausible but entirely fictional legacy-format example: 123456789 (9 numeric digits). A fictional current-format example illustrating a mixed alphanumeric style: C1234567.

Key Things to Know

  • No checksum digit: the US Passport Validator checks length and character-set plausibility only, unlike VIN's or CUSIP's built-in check digits.
  • Changes on every renewal: a new passport number is issued with each renewal or replacement — old numbers are permanently retired, unlike a persistent identifier such as an NPI.
  • Books and cards are separate documents: a passport book and passport card issued to the same person carry different, independently numbered identifiers.
  • Distinct from a Known Traveler Number: a passport number identifies the travel document itself; a Known Traveler Number identifies trusted-traveler program enrollment for expedited screening.
  • Verified via the MRZ at borders: border control systems read the passport number together with the rest of the machine-readable zone (name, date of birth, expiration date) rather than relying on the number alone.
  • Sensitive but not as broadly used as an SSN: a passport number is tied to a specific travel document rather than being a general-purpose identity number, so its exposure risk is narrower than an SSN leak.

Related Terms

Known Traveler NumberKnown Traveler Number (KTN)SSNUS Social Security Number

Frequently Asked Questions

Historically, US passport book numbers were 9 digits, matching the length of an [SSN](/glossary/ssn/), but the State Department has since moved to formats that can include letters as well as digits, particularly for newer passport books and passport cards. You can check a number's plausibility against current format rules with the [US Passport Validator](/validators/us-passport-validator/).
No, a US passport number has no publicly documented checksum digit — validation is limited to confirming length and the allowed character set (numeric-only for older books, alphanumeric for newer issuances). Confirming that a specific number is a real, currently valid passport requires checking with the US Department of State, which validators cannot do.
A US passport book is required for international air travel and grants full global travel privileges, while a US passport card is a cheaper, wallet-sized alternative valid only for land and sea travel between the US and Canada, Mexico, Bermuda, and the Caribbean. The two documents have separate, non-interchangeable passport numbers even when issued to the same person.
No. A passport number identifies a specific travel document issued by the State Department, while a [Known Traveler Number](/glossary/known-traveler-number/) identifies enrollment in a trusted-traveler program like TSA PreCheck or Global Entry. International travelers commonly provide both when booking a flight.
Yes, each time a US passport is renewed or replaced, a new passport number is issued along with the new physical document — the number is not reused from the previous passport. This means historical passport numbers become invalid once superseded by a renewal.