First Class Mail: Size Limits, Delivery Times & Tracking

First-Class Mail is the USPS service for letters, postcards and large envelopes (flats) weighing up to 13 ounces, delivered in 1–5 days anywhere in the U.S. Standard letters can weigh up to 3.5 ounces, flats up to 13 ounces, and the service includes free mail forwarding and return to sender, but no tracking unless you add an extra service such as Certified Mail.

First-Class Mail is still the Postal Service’s biggest product for correspondence: USPS handled about 42.0 billion First-Class Mail pieces in fiscal year 2025, down 5% from the year before. Packages are a different story. The old First-Class Package Service was folded into USPS Ground Advantage in July 2023, so today First-Class Mail means envelopes and cards, not boxes.

What Can You Send by First-Class Mail?

First-Class Mail covers three shapes, and each has its own size and weight limits set in the USPS Domestic Mail Manual. A piece that exceeds the limits for its shape moves up to the next shape and is priced as that shape.

The minimum for any letter or card is 5 inches long, 3-1/2 inches high and 0.007 inch thick. A letter that is square, rigid, lumpy or has clasps can’t run through USPS sorting machines, so it pays a nonmachinable surcharge even though it is within the letter limits. Our guide to how heavy a letter can be for one First-Class stamp explains how weight adds up, and for oversized envelopes see how many stamps you need for a large envelope.

How Long Does First-Class Mail Take?

USPS lists First-Class Mail at 1–5 days for delivery within the United States. Mail between nearby cities usually arrives in 1–3 days, while cross-country mail and mail to Alaska, Hawaii and U.S. territories takes longer, toward the end of that range.

There is no guaranteed delivery date and no refund if a letter arrives late. If timing matters, USPS Priority Mail Express is the only USPS service with a money-back guarantee, and our guide to Priority Mail Express covers its overnight and 2-day commitments.

Does First-Class Mail Include Tracking?

No. USPS states that First-Class Mail letters and flats do not include tracking or insurance. To get proof of mailing or delivery, add an extra service at the Post Office:

• Certified Mail: gives you a mailing receipt and a tracking number with the date and time of delivery or attempted delivery.
• Return Receipt: added to Certified Mail, it gives you the recipient’s signature, on a green card or by email.
• Certificate of Mailing: official proof that you mailed the piece on a given date, without delivery tracking.
• Registered Mail: the most secure USPS option, with chain-of-custody handling and insurance for valuable items.

If you need to stop or reroute a tracked piece after mailing, our guide to USPS Package Intercept explains which items qualify.

What Services Come Free With First-Class Mail?

First-Class Mail includes forwarding and return service at no extra charge. When someone files a change of address, USPS forwards their First-Class Mail free for 12 months, as our USPS change of address guide explains. If a piece can’t be delivered or forwarded, USPS returns it to the sender free, which is why a clear return address on every envelope matters.

First-Class Mail also moves ahead of USPS Marketing Mail in processing. Marketing Mail is cheaper bulk mail, but it isn’t forwarded or returned unless the sender pays for that service.

How Do You Pay for First-Class Mail Postage?

Most people pay with Forever stamps. A Forever stamp always covers one 1-ounce First-Class letter at whatever the price is on the day you mail it, so stamps bought years ago are still good after a price change. Our explainer on whether Forever stamps expire covers the details, and postcards need a postcard stamp or a Forever stamp, as our guide to postcard stamps explains.

Heavier letters and flats need additional-ounce postage, and nonmachinable pieces need the surcharge on top. USPS publishes current First-Class Mail prices in its official price list, Notice 123, and usually adjusts mailing prices once or twice a year, so check the notice before buying a large supply of extra-ounce or nonmachinable stamps.

One rule applies at the mailbox: USPS security rules require heavier or thicker pieces that carry only stamps to be handed to a clerk at a Post Office counter rather than dropped in a blue collection box, so take bulky stamped envelopes inside.

First-Class Mail vs Priority Mail and Ground Advantage

First-Class Mail is for flat mail, while packages go by Ground Advantage or Priority Mail. Our side-by-side guide to Priority Mail vs First-Class goes deeper, but the table shows the main differences.

Anything thicker than 3/4 inch, rigid or box-shaped is a package, even if it weighs only a few ounces. Light packages under 1 lb are the usual job of USPS Ground Advantage, the service that replaced First-Class Package Service. For faster delivery with included insurance, see the USPS Priority Mail guide, and for flat-priced boxes compare USPS Flat Rate Box sizes.

Package postage is where online labels save the most. ParcelPath sells USPS Ground Advantage and Priority Mail labels at up to 89% off USPS retail, free and with no subscription. You can compare live USPS and UPS package rates in the ParcelPath calculator, then hand the package to your carrier with a free USPS pickup. Our overview of USPS service tiers and transit times covers every option.

Can You Send First-Class Mail Internationally?

Yes. First-Class Mail International carries letters, postcards and flats to almost every country, and a single Global Forever stamp covers a 1-ounce letter or a postcard to any country that accepts mail from the U.S. Heavier international envelopes need extra postage, and USPS service to some countries is limited or suspended, so check USPS International Service Alerts before mailing.

Small international packages go by First-Class Package International Service, which takes packages up to 4 lbs and requires a customs form.

Frequently Asked Questions

What is the weight limit for First-Class Mail?

First-Class Mail letters can weigh up to 3.5 ounces and large envelopes (flats) up to 13 ounces. A letter heavier than 3.5 ounces is mailed at the flat price, and anything over 13 ounces has to go as a package, usually by USPS Ground Advantage or Priority Mail, both of which include tracking.

How long does First-Class Mail take to arrive?

USPS lists First-Class Mail at 1–5 days within the United States. Local and regional mail often arrives in 1–3 days, while cross-country mail and mail to Alaska, Hawaii and U.S. territories can take the full 5 days. USPS doesn’t guarantee a delivery date for First-Class Mail.

Can I track a First-Class letter?

Not on its own. First-Class Mail letters and flats don’t include USPS Tracking. To get a tracking number and proof of delivery, add Certified Mail at the Post Office, and add Return Receipt if you also want the recipient’s signature. Registered Mail adds secure handling and insurance for valuables.

Is First-Class Package Service still available?

No. USPS retired First-Class Package Service on July 9, 2023, and merged it with Retail Ground and Parcel Select Ground into USPS Ground Advantage. Ground Advantage carries packages up to 70 lbs in 2–5 days with tracking and some insurance included. First-Class Mail now covers only letters, postcards and flats.

Is First-Class Mail forwarded when someone moves?

Yes. When a recipient files a change of address, USPS forwards First-Class Mail free for 12 months. If the piece can’t be delivered or forwarded, USPS returns it to the sender at no charge, so always include a return address on the envelope.

Sources

• USPS Domestic Mail Manual 101: Physical standards for letters, cards and flats
• USPS: Mail and shipping services comparison (delivery times, tracking, weight limits)
• USPS: First-Class Mail
• USPS: Forward mail and change of address
• USPS Notice 123: Price list
• USPS: Fiscal year 2025 results (First-Class Mail volume)
• USPS: First-Class Mail International

First-Class Mail is one tier in the wider USPS lineup, and our roundup of shipping services and solutions compares it with the main package carriers. For everything else USPS offers, start at our USPS shipping hub.

Part of our USPS Services guide. Related: Ground Advantage, USPS Priority Mail, Priority Mail Express.