USPS mail classes are the seven categories the Postal Service uses to price and route domestic mail: First-Class Mail, Priority Mail, Priority Mail Express, USPS Ground Advantage, USPS Marketing Mail, Periodicals, and the Package Services pair of Media Mail and Library Mail. Each class has its own price, delivery window, weight limit, and rules about what can go inside. Picking the wrong one means overpaying, waiting longer than you needed to, or having the piece kicked back for containing something it shouldn’t.
The quick way to think about it: letters and correspondence go First-Class, fast packages go Priority or Priority Express, everyday packages go Ground Advantage, bulk advertising goes Marketing Mail, subscription publications go Periodicals, and books or recordings go Media Mail. The rest of this article walks each class in enough detail to make the call.
First-Class Mail
First-Class is the standard service for letters, bills, invoices, credit cards, and business correspondence. Some items are required to travel this way: anything handwritten or typewritten, bills and account statements, credit cards, and sealed personal correspondence must go First-Class at a minimum.1Postal Explorer. First-Class Mail
A one-ounce stamped letter currently costs $0.78, with each additional ounce adding $0.29. Metered postage drops the first-ounce rate to $0.74.2United States Postal Service. Notice 123 Price List USPS has proposed raising the stamp price to $0.82 in July 2026.3United States Postal Service. USPS Recommends New Prices for July
The class comes in three shapes: letters up to 3.5 ounces, large envelopes (flats) up to 13 ounces, and small packages up to 13 ounces.1Postal Explorer. First-Class Mail Anything over 13 ounces moves to Priority Mail. The 13-ounce ceiling applies to retail and commercial mailers alike; businesses don’t get a higher limit.4United States Postal Service. Notice 123 Price List Delivery runs one to five business days, and the class includes free forwarding if the recipient has moved and free return to sender if the piece is undeliverable.5Postal Explorer. Classes of Mail
Priority Mail
Priority Mail is what you use when First-Class is too slow, or when your item weighs more than 13 ounces. Delivery is one to three business days for most domestic destinations, and packages can weigh up to 70 pounds with a combined length and girth of up to 108 inches.6USPS. Priority Mail
The easiest pricing option is Flat Rate. USPS provides free Flat Rate envelopes and boxes; fill them with anything up to 70 pounds and the price is fixed regardless of distance. A Flat Rate Envelope runs $11.95 at the Post Office counter or $10.30 with commercial pricing.7USPS. Postage Rates and Prices Every Priority shipment comes with $100 of insurance and USPS Tracking at no extra charge. For packages larger than one cubic foot, USPS calculates a dimensional weight by multiplying length, width, and height and dividing by 166, then bills whichever is higher: the actual weight or the dimensional weight.6USPS. Priority Mail
Priority Mail Express
Priority Mail Express is the fastest domestic service USPS offers. Delivery is guaranteed in one to three days by 6 PM, and there’s a money-back guarantee if USPS misses the commitment.8USPS. Priority Mail Express That refund is the main reason to pay for Express over standard Priority.
Prices start at $33.00 at the Post Office. A Flat Rate Envelope costs $33.25 retail or $28.80 commercial.8USPS. Priority Mail Express The service runs every day of the year with limited exceptions, and Sunday and holiday delivery is available in many major markets for an added fee. Shipments include $100 of insurance and tracking.
USPS Ground Advantage
Ground Advantage replaced several older USPS services in 2023 and is now the main option for packages that don’t need Priority speed. It handles items up to 70 pounds with a two-to-five-day delivery window. Every shipment includes tracking and $100 of insurance, with additional coverage available up to $5,000.9USPS. Ground Advantage
Pricing starts at $7.30 retail or $5.09 commercial.7USPS. Postage Rates and Prices Items under 15.999 ounces are priced in tiered brackets (up to 4 oz, 8 oz, 12 oz, and 15.999 oz); heavier items are charged by the pound. Ground Advantage also picks up oversize First-Class envelopes that fail flat dimensions: anything longer than 15 inches, taller than 12 inches, thicker than three-quarters of an inch, or too rigid or lumpy to qualify as a flat routes through Ground Advantage instead.9USPS. Ground Advantage The service includes free forwarding, return to sender, and free package pickup from your home or office.
USPS Marketing Mail
Marketing Mail is the bulk-rate class for advertisements, flyers, catalogs, newsletters, and small merchandise shipments. It’s cheaper than First-Class with two trade-offs: slower delivery with no guaranteed timeline, and a volume minimum. Every mailing must contain at least 200 pieces or weigh at least 50 pounds total.10Postal Explorer. 240 Commercial Mail USPS Marketing Mail
Content rules are strict. Anything that counts as personal correspondence, including handwritten notes, bills, and account statements, cannot travel as Marketing Mail and must go First-Class.11Postal Explorer. USPS Marketing Mail Eligibility Each piece must weigh less than 16 ounces. Marketing Mail does not include free forwarding or return service; undeliverable pieces are discarded unless the sender prints an ancillary service endorsement on the mailpiece requesting a different outcome.
Periodicals
Periodicals is reserved for newspapers, magazines, and similar publications whose main purpose is delivering information to a subscriber or requester list. To qualify, a publication must be issued at regular intervals of at least four times a year from a known office of publication, and must consist of printed sheets.12PostalPro. Periodicals Publishers need formal USPS authorization before mailing at Periodicals rates. The class offers competitive pricing and includes free forwarding for 60 days after a subscriber moves.5Postal Explorer. Classes of Mail
Media Mail and Library Mail
These two Package Services classes offer the cheapest shipping rates USPS provides, in exchange for tight limits on what you can put inside.
Media Mail
Media Mail carries educational and cultural materials. Eligible items include books of at least eight pages consisting entirely of reading matter or scholarly bibliography; sound and video recordings such as CDs, DVDs, vinyl, and player piano rolls; 16-millimeter or narrower positive film prints in final form (not films sent to or from commercial theaters); printed music in bound or sheet form; playscripts and manuscripts for books, periodicals, or music; printed objective tests and their accessories used by educational institutions; single-sheet educational reference charts that convey information mainly through graphs, diagrams, or tables; and computer-readable media with accompanying prerecorded content and guides.
The core prohibition is advertising. Media Mail packages may not contain advertising materials. Books can include incidental announcements of other books, and sound recordings can include announcements of other recordings, but that’s the limit. Comic books don’t qualify at all.13Postal Explorer. 170 Retail Mail Media Mail and Library Mail USPS employees can open Media Mail packages to inspect the contents; if they find non-qualifying items, the package gets returned or assessed additional postage. Maximum weight is 70 pounds.14USPS. Mail and Shipping Services
Library Mail
Library Mail runs cheaper than Media Mail but restricts who can use it. Each piece must show the name of a qualifying institution (a school, college, university, public library, museum, herbarium, or qualifying nonprofit) in either the delivery or return address.13Postal Explorer. 170 Retail Mail Media Mail and Library Mail
Eligible items include books, printed music, bound academic theses, periodicals, sound recordings, museum specimens, teaching aids, and scientific instruments. Library Mail can travel between qualifying institutions and individual recipients, as long as the individual has no financial interest in selling or promoting the materials.13Postal Explorer. 170 Retail Mail Media Mail and Library Mail Content rules are slightly broader than Media Mail (scientific kits, film catalogs, and interpretive museum materials all qualify), but the sender and recipient rules are much narrower.
How to Choose
Start with what you’re sending. A personal letter, bill, or anything handwritten must go First-Class or Priority. If your piece is under 13 ounces and contains correspondence, First-Class is the only option. Cross 13 ounces and you’re choosing between Priority Mail and Ground Advantage.
For packages, that choice comes down to speed against cost. Priority delivers in one to three days and starts at $10.30 commercially; Ground Advantage takes two to five days and starts at $5.09.7USPS. Postage Rates and Prices Both include tracking and $100 of insurance. If you’re shipping books or recordings and can wait longer, Media Mail beats both on price by a wide margin, but only if every item in the box is on the eligible list.
Priority Mail Express earns its price when you need the delivery guarantee. Starting at $33.00, it’s overkill for everyday shipping, but the money-back guarantee is the point for time-sensitive documents and irreplaceable items.8USPS. Priority Mail Express
Marketing Mail and Periodicals only enter the picture for businesses and publishers who meet the volume and content rules. If you’re mailing under 200 pieces, or mailing anything that reads as personal correspondence, neither class is available to you.
Content Restrictions to Watch For
Every class has content rules, and some restrictions cut across all of them. Hazardous materials, including lithium batteries, aerosols, perfumes containing alcohol, nail polish, paints, and dry ice, have special packaging, labeling, and documentation requirements. Items containing visible liquid mercury, such as old thermometers and barometers, are prohibited outright. Anything with a battery or a flammable component should be checked against the product’s Safety Data Sheet for its classification, then packaged and labeled to match.
Ground Advantage is the designated service for hazardous materials restricted to ground transportation.9USPS. Ground Advantage Sending restricted items through air-transported Priority Mail or Express without proper documentation can result in the package being seized or returned, and potentially civil penalties.