The Postal Service divides mail into different services, called "classes." Each class of mail has different features, service levels, postage prices, and presort requirements.
For most of your mailings, the content of the material and postage will determine the class of mail you select. To learn more about each class of mail—including what can be mailed, the minimum and maximum weights and sizes, and the number of pieces needed for commercial prices—just click on the name of the class of mail. Not sure which class of mail is right for your mailing? Look at the matrix below to determine what class of mail best matches your priorities.
If you are unsure about what class your mailpiece will—or should—be, contact your business mail entry unit for advice.
Priority Mail Express: Anything mailable, letters, merchandise.
Priority Mail: Anything mailable, bills, invoices, personal correspondence, merchandise.
First-Class Mail: Anything mailable, bills, invoices, personal correspondence, merchandise.
Periodicals: Newsletters, magazines; (formal authorization needed).
Standard Mail: Advertisements, circulars, newsletters, small parcels, merchandise.
Package Services and USPS Retail Ground: Merchandise, catalogs, printed material, computer media.