USPS Flat Rate shipping lets you send anything that fits inside an official USPS envelope or box for one fixed price, no matter the weight (up to 70 pounds) or the domestic destination. Prices in 2026 start at $11.95 for a standard Flat Rate Envelope and top out at $31.50 for a Large Flat Rate Box at the counter. Every shipment includes tracking, up to $100 of insurance, and two- to three-day delivery.
The catch is that you have to use the USPS-branded container. Pack your own box, even one the same size, and USPS charges regular Priority Mail rates based on weight and zone instead.
Flat Rate Containers and 2026 Prices
USPS offers three envelopes and four boxes, all free from any post office or shipped to your door through the USPS Postal Store. The prices below took effect January 18, 2026, and the second figure is the commercial rate you get by buying postage online instead of at the counter.1Postal Explorer. Notice 123 – Price List
Envelopes
- Flat Rate Envelope, 12.5 by 9.5 inches — $11.95 retail / $10.30 commercial. Suits documents, photos, and thin items.
- Legal Flat Rate Envelope, 15 by 9.5 inches — $12.25 retail / $10.80 commercial. The extra length fits legal-size documents.
- Padded Flat Rate Envelope, 12.5 by 9.5 inches with cushioned lining — $12.95 retail / $11.10 commercial. Good for small electronics or jewelry.
Boxes
- Small Flat Rate Box, 8-11/16 by 5-7/16 by 1-3/4 inches — $12.65 retail / $11.20 commercial.
- Medium Flat Rate Box, top-loading, 11-1/4 by 8-3/4 by 6 inches — $22.95 retail / $19.60 commercial. Deeper profile for books, shoes, or stacked goods.
- Medium Flat Rate Box, side-loading, 14 by 12 by 3-1/2 inches — $22.95 retail / $19.60 commercial. Wider and flatter for framed photos or clothing.
- Large Flat Rate Box, 12-1/4 by 12 by 6 inches — $31.50 retail / $28.70 commercial.
- APO/FPO/DPO Flat Rate Box, same size as the Large — $30.15 retail / $27.40 commercial, discounted for military addresses.
Both Medium boxes cost the same, so choose whichever shape fits your item better. Dimensions listed are outside measurements; inside space runs roughly half an inch smaller in each direction.
Getting the Commercial Rate
Commercial pricing is not reserved for businesses. You qualify by paying for postage through any of these channels rather than at the counter:
- USPS Click-N-Ship, the free label tool on usps.com.
- Approved PC Postage products such as Stamps.com, Pirate Ship, or ShipStation.
- A permit imprint account.
- USPS-approved postage meters that transmit data electronically.2Postal Explorer. 220 Commercial Mail Priority Mail
For most people, Click-N-Ship is the simplest route. You print the label at home, skip the counter line, and save several dollars per package. The gap between retail and commercial reaches $2.80 on a Large box and $3.35 on a Medium.
Weight Cap and the Closure Rule
Domestic Flat Rate shipments can weigh up to 70 pounds. Anything heavier is nonmailable entirely, not simply rerouted to another service.3United States Postal Service. Parcel Size, Weight and Fee Standards
The rule most senders actually hit is closure. The box flaps have to close within their normal folds. Tape reinforcing the seams is fine. Slitting the sides, adding cardboard extensions, or reshaping the box to squeeze in an oversized item is not. If a clerk spots that kind of modification, the package gets reclassified to standard Priority Mail and repriced by weight and zone. A small bulge in the lid is acceptable, but nothing can protrude from the container, and wrapping tape all the way around a box to hold it shut is a giveaway that will trigger reclassification.4United States Postal Service. DMM Notice: Proper Use of Flat Rate Containers
What You Can’t Ship
The same prohibited-item rules that apply across USPS mail apply to Flat Rate. Explosives, flammable gases, and poisonous substances are off-limits. Knowingly mailing a prohibited item can bring fines and up to one year in prison. If the item is sent with intent to injure someone, the penalty rises to up to 20 years.5Office of the Law Revision Counsel. 18 USC 1716 – Injurious Articles as Nonmailable
Lithium Batteries
Batteries installed in or packed with equipment can ship by air or ground. Loose individual batteries can only travel by ground. Each cell is capped at 20 watt-hours, each battery at 100 watt-hours, and a mailpiece can hold no more than eight cells or two batteries.
Most lithium-ion shipments also need a DOT-approved lithium battery mark on the address side showing the UN number: UN3481 for batteries packed with equipment, UN3480 for standalone batteries. Loose batteries need a “Surface Mail Only” marking. Used, damaged, or defective electronics with lithium batteries inside must be marked “Restricted Electronic Device” and shipped surface-only.6Postal Explorer. Publication 52 – Appendix C – USPS Packaging Instruction 9D
Liquids
Non-hazardous liquids are allowed, but any non-metal container holding more than four ounces needs triple packaging: absorbent material around the bottle sufficient to soak up the full contents if it breaks, a leakproof secondary container such as a sealed plastic bag, and the outer shipping box. Screw caps need at least one and a half turns to count as secure. Push-down friction tops alone are not acceptable and require a locking ring or an additional sealed outer container. The outside of the package must be marked to show it contains liquid and include orientation arrows.7USPS Postal Explorer. Publication 52 – Hazardous, Restricted, and Perishable Mail
Insurance and Tracking Included
Every Priority Mail Flat Rate shipment includes up to $100 of insurance against loss, damage, or missing contents at no extra cost, along with USPS tracking. The tracking barcode is generated automatically when you buy postage online or at the counter, and the barcode is what triggers the insurance coverage.8United States Postal Service. Shipping Insurance and Delivery Services
If your item is worth more than $100, additional insurance is available when you create the label. Signature Confirmation and USPS Tracking Plus can also be added at the counter or through Click-N-Ship.
Dropping Off Your Package
Once your package is sealed and labeled, you have a few options. The post office counter is the most direct: a clerk verifies Flat Rate status and gives you a receipt. Self-service kiosks at many post offices accept labeled packages outside regular business hours.
You can also schedule a free Package Pickup through usps.com, and your regular carrier will collect the package from your home or office the next delivery day.9United States Postal Service. Package Pickup and Pickup on Demand Blue USPS collection boxes accept packages that fit through the slot, which usually means Small Flat Rate Boxes and envelopes. Medium and Large boxes have to go through a counter, kiosk, or carrier pickup.
Shipping to Military Addresses
Packages sent to APO, FPO, and DPO addresses ship at domestic Flat Rate prices even when the destination is overseas. The dedicated APO/FPO/DPO Flat Rate Box costs $30.15 retail ($27.40 commercial), which is $1.35 less than the standard Large box at the counter despite being the same interior size.10United States Postal Service. Priority Mail
Military shipments still need a customs form even though they are priced domestically. You can fill out PS Form 2976-R as a worksheet and bring it to the counter, where a clerk enters the information into the system and prints the actual customs label. The paper form on its own is not a valid customs declaration.11Postal Explorer. International Mail Manual – 123 Customs Forms and Online Shipping Labels You can also create the customs form online through Click-N-Ship before heading to the post office.12United States Postal Service. Military and Diplomatic Mail
International Flat Rate Works Differently
Priority Mail International Flat Rate uses the same idea, but the price varies by destination. USPS sorts countries into eight price groups. A Large Flat Rate Box to Canada (Price Group 1) runs $75.15; the same box to Australia (Price Group 8) costs $132.05.13Postal Explorer. USPS Notice 123 – January 2026 Price Change
Weight limits are tighter too. Envelopes and Small Flat Rate Boxes cap at four pounds; Medium and Large boxes at 20 pounds. Individual countries may impose lower limits.14United States Postal Service. Priority Mail International
Every international Flat Rate shipment requires a customs declaration, and all customs forms must now be generated electronically. Handwritten forms are no longer accepted. Create one through Click-N-Ship, the USPS Customs Form Online tool, or approved third-party shipping software, or bring a completed PS Form 2976-R to the counter as a worksheet for the clerk.11Postal Explorer. International Mail Manual – 123 Customs Forms and Online Shipping Labels
When You Need It Faster: Express Flat Rate
Priority Mail Express offers one- to three-day delivery with a money-back guarantee. Express Flat Rate is envelope-only. There are no Express Flat Rate boxes.
- Flat Rate Envelope: $33.25 retail / $28.80 commercial
- Legal Flat Rate Envelope: $33.50 retail / $29.10 commercial
- Padded Flat Rate Envelope: $34.15 retail / $29.35 commercial
The envelopes are the same dimensions as the Priority Mail versions. What you pay extra for is speed and the refund policy.1Postal Explorer. Notice 123 – Price List
If USPS misses the guaranteed delivery date, you can request a full postage refund. File no sooner than two days and no later than 30 days after the mailing date. The guarantee does not apply when the delay was caused by weather, government action, or flight cancellations, and it does not cover shipments to or from Alaska, Hawaii, or most U.S. territories.15United States Postal Service. Priority Mail Express Service