For the ones you mention that have 22 digits, the first 8 digits (if memory serves) identify the class of mail service and other metadata. So that leaves you wi

For the ones you mention that have 22 digits, the first 8 digits (if memory serves) identify the class of mail service and other metadata. So that leaves you with 10^14 at most, assuming there’s no encoding overhead / check digits. > USPS tracking numbers are at least 22 digits long Actually, that’s wrong. There are shorter ones. Examples: 82 000 000 00 - Global Express Guaranteed EC 000 000 000 US - Priority Mail Express International CP 000 000 000 US - Priority Mail International There’s also foreign shipped packages that will follow various standards that aren’t 22 digits, yet are still technically a valid USPS tracking number.