USPS tracking numbers, also known as label or receipt numbers, are read in a straightforward manner right off the package receipt. USPS tracking numbers range in length from 16 to 34 digits depending on the mail class used for shipping. Some tracking numbers also contain letters.
To track packages, a user can enter the tracking number from their package receipt at the USPS website into their tracking tool to get information on the status of the package. The level of information depends on the mail class and any extra tracking services that were purchased. Spaces may be entered or left out when inputting the tracking number without affecting the results.