UPU S10 Standard

The UPU S10 standard is a rule and recommendation established by the Universal Postal Union (UPU) regarding the structure and format of international postal tracking numbers. The UPU is a specialized agency of the United Nations that coordinates the postal policies of member countries worldwide. The UPU S10 standard defines the requirements and specifications that tracking numbers must meet to be correctly recognized and processed in the international postal system for the postal services of the original and destination countries.

UPU S10 Format

The UPU S10 standard defines the format for international postal tracking numbers and combines letters and numbers. The S10 UPU format is the alphanumeric characters required for S10 identifiers, consisting of XX123456789YY (2 alphabetic characters followed by nine numeric characters and two alphabetic characters). The format is commonly called "A2-N9-A2" or simply "2-9-2". Any bar code containing two alpha characters, nine numeric characters, and two alphabetic characters may be considered to be in S10 format, whether or not it complies with the data content requirements of this standard.

Here is an example of the tracking number format based on the UPU S10 standard

Tracking Number: AG018300045CN

  • AG - Service indicator;
  • 01830004 - Serial number;
  • 5 - Check digit;
  • CN - Country code.

Service indicator

The service indicator consists of two alphabetic characters and is intended for universal use between postal services, the first character indicates the type of mail product or service, and the second character is assigned by the operator of the origin from the range of valid values.

  • Express Mail Service (EMS)
    • EA–EZ, the use of EX–EZ requires a bilateral agreement;
  • Letter Post
    • LA–LZ, Letter post tracked, the use of LZ requires a bilateral agreement;
    • MA–MZ, M bags;
    • QA–QM, IBRS (International Business Reply Service)
    • RA–RZ Letter post registered, the use of RZ requires a bilateral agreement;
    • UA–UZ, Letter-post items containing goods, the use of UZ requires bilateral agreement;
    • VA–VZ, Letter post insured, the use of VZ requires a bilateral agreement;
  • Parcel Post
    • CA–CZ Parcel posturing of CZ requires bilateral agreement. A CV for insured parcels is not required, but if the service indicator CV is used, it is recommended to be used only on insured parcels.
    • HA–HZ ECOMPRO parcels, using HX–HY requires multilateral agreement, and using HZ requires bilateral agreement.
  • Other Codes allocated for domestic/bilateral/multilateral use only
    • AV–AZ
    • BA–BZ
    • DA–DZ
    • GA
    • GD
    • NA–NZ
    • PA–PZ
    • ZA–ZA

Serial number

The serial number must be precisely eight digits long. Zeros are used when eight digits are required. Therefore, any value between 00000000 and 99999999 is considered a valid serial number.

Check digit

A check digit is a number resulting from an arithmetic calculation and is used to help detect substitution and transposition errors that may occur during data collection. For S10 identifiers, the check digit is the 11th character, determined using a weighted modulo 11 algorithm.

Algorithm for calculating the control check number:

  1. multiply the serial number digits by the weighting factors 86, 42, 3, 5, 9, 7 (that is, multiply the first digit by 8, the second by 6, the third by 4, and so on until the last by 7);
  2. calculate the sum of weighted values;
  3. divide this amount by 11 (eleven) to get the remainder;
  4. subtract the remainder from 11;
  5. if the result is between 1 and 9, use the result as a check digit;
  6. if the result is 10, use 0 as the check digit;
  7. Use five as the check digit if the result is 11.

For example, AG018300045CN, Serial number: 01830004

  1. (0 * 8) + (1 * 6) + (8 * 4) + (3 * 2) + (0 * 3) + (0 * 5) + (0  * 9) + (4 * 7) = 72
  2. 72 % 11 = 72 - 11 * 6 = 6
  3. 11 - 6 = 5

Country code

This should be the two-character ISO 3166-1 (2 chars) code representing the UPU member country that issued the S10 identifier.

For example

  • CN - China;
  • JP - Japan;
  • US - USA.

Issuance and Management of S10 Identifiers

S10 identifiers ending in a specific ISO 3166-1 country code should only be issued with the authorization of a single organization designated by a member country of the UPU. For example, in the USA, it is the national postal operator USPS; in China, it is the China Post; and in the UK, it is Royal Mail.

The postal service designated by a member country of the UPU oversees the issuance and use of S10 identifiers among all operators administered by that member country of the UPU. They must ensure no S10 tracking number is reissued within 12 calendar months, although the recommended duration is 24 months.


Our free online validator provides an effortless way to validate tracking numbers according to the UPU S10 Standard. By simply entering the tracking number, you can quickly obtain information about the type of postal mail, the origin country, and the postal service that issued the tracking number. This service ensures that you can verify the authenticity and legitimacy of the tracking number, giving you peace of mind and confidence in your package's status and delivery. Whether you're a regular online shopper or a business owner managing shipments, our tracking number validator is a valuable tool for ensuring the accuracy and reliability of your tracking information.