USPS Priority Mail Flat Rate ships a package to any U.S. address for one fixed price based on the container you choose, no matter the weight (up to 70 pounds) or the distance. A small flat rate box costs $12.65 at the retail counter and a large runs $31.50, with lower prices online. Every shipment includes tracking, 2- to 3-business-day delivery, and $100 of insurance at no extra cost. The catch: you have to use official USPS flat rate packaging, which the Postal Service provides for free.
2026 Flat Rate Prices
What you pay depends on where you buy the label. Retail prices apply at the post office counter. Commercial prices apply when you print a label at home through Click-N-Ship, which only requires a free USPS.com account.
- Flat Rate Envelope: $11.95 retail / $10.30 commercial
- Legal Flat Rate Envelope: $12.25 retail / $10.80 commercial
- Padded Flat Rate Envelope: $12.95 retail / $11.10 commercial
- Small Flat Rate Box: $12.65 retail / $11.20 commercial
- Medium Flat Rate Box: $22.95 retail / $19.60 commercial
- Large Flat Rate Box: $31.50 retail / $28.70 commercial
The commercial discount is real: printing your own label for a large flat rate box saves $2.80 per package over the counter price. Businesses that opt into the USPS Business Rate Card can save more.
Packaging Sizes and What Fits
USPS provides all flat rate packaging free. Pick it up at any post office or order it through the USPS Postal Store for delivery. Every container carries flat rate branding so clerks apply the right price. Your own box does not qualify, even if it’s the same size.
Envelopes
- Flat Rate Envelope, 12½” × 9½”, for documents, contracts, and photos.
- Legal Flat Rate Envelope, 15″ × 9½”, three inches wider for legal-size paperwork.
- Padded Flat Rate Envelope, 12½” × 9½”, bubble-lined for small electronics or jewelry.
Boxes
- Small Flat Rate Box, 8⅝” × 5⅜” × 1⅝” inside. Phone cases, cables, a few thin books.
- Medium Flat Rate Box, top-loading, 11″ × 8½” × 5½” inside. The deeper medium option for clothing or shoes.
- Medium Flat Rate Box, side-loading, 13⅝” × 11⅞” × 3⅜” inside. Wider and shallower for flat items like board games.
- Large Flat Rate Box, 12″ × 11¾” × 5½” inside. The biggest flat rate option, good for heavy or bulky gift sets.
The two medium boxes hold roughly the same volume distributed differently. Pick the top-loader for tall items and the side-loader for flat ones. Outside dimensions run slightly larger than the interior figures above.
The Rule That Trips People Up
Flat rate refers to the price, not the shape of the package. The container has to close within its normal manufactured folds. Bulging is fine. If the flaps close where they were designed to close, the package ships at the flat rate price, even if it looks stuffed.
Cutting, reshaping, or reconstructing the box to fit something larger voids flat rate pricing. Postal workers will reclassify the package as weight-and-zone Priority Mail, which can cost more.
The 70-pound weight ceiling applies to every flat rate container. You’ll usually run out of space long before running out of weight allowance, but it matters for dense items like tools or metal parts.
Delivery Speed and What’s Included
Priority Mail Flat Rate typically arrives in 2 to 3 business days. USPS gives you an expected delivery date at checkout, but that date is not guaranteed and does not come with a refund for late arrival. If you need a money-back guarantee, Priority Mail Express is a separate, more expensive service.
Priority Mail adds no surcharges for fuel, residential delivery, rural delivery, or Saturday delivery. Saturday counts as a normal delivery day at no extra cost, which is unusual among carriers.
Every shipment includes a tracking number (typically 22 digits for domestic Priority Mail) that you can enter at usps.com/tracking or in the USPS mobile app. Delivery confirmation is automatic. Signature Confirmation costs $4.95 at the counter or $3.95 through Click-N-Ship if you want a signature on file.
Insurance of $100 against loss, damage, or missing contents is built into every domestic flat rate shipment. You can buy additional coverage at the time you purchase postage if the contents are worth more.
How to Ship One
Get the packaging first, either from a post office or through the Postal Store online. Pack your items so the container closes on its own folds. Address it clearly, with a return address, and you’re ready to pay for postage.
Two ways to do it:
- Click-N-Ship online. Log into usps.com, enter shipment details, print your label at home, and drop the package at a post office, in a blue collection box if it fits, or leave it for pickup.
- At the post office. Bring the sealed, addressed package to the counter and pay the retail rate. A clerk applies the label and accepts the package.
Free package pickup is the easiest option many people skip. Schedule it online, leave the package where your carrier can find it, and it goes out on the next delivery day.
Filing a Claim if It’s Lost or Damaged
File a claim at usps.com or by mailing PS Form 1000. The deadlines are strict:
- Damaged or missing contents: file as soon as possible, and no later than 60 days from the mailing date.
- Lost packages: file no sooner than 15 days after mailing, and no later than 60 days.
You’ll need proof of value (receipt, invoice, or credit card statement), your mailing receipt or electronic label record, and, for damage claims, the original packaging and the contents. USPS may ask to inspect damaged items at your local post office. Throwing away the box before filing is the fastest way to get denied.
Insurance does not cover consequential losses, delivery delays, spoilage, concealed damage, improperly packaged items, items too fragile for normal handling, or prohibited items.
What You Can’t Ship
Some items are banned from all domestic mail:
- Ammunition and explosives
- Gasoline and other fuels
- Liquid mercury
- Marijuana, including state-legal medical marijuana
- Airbags
- Strike-anywhere matches
Knowingly mailing dangerous materials carries a civil penalty of at least $250 and up to $100,000, plus cleanup costs and possible criminal charges.
Lithium batteries have their own rules. Batteries installed in a device can ship by air if each cell is under 20 watt-hours and each battery under 100 watt-hours, with a limit of eight cells or two batteries per package. Loose lithium-ion batteries not installed in a device ship only by ground and cannot exceed 5 pounds per package. Damaged, defective, or recalled batteries are banned outright.
Liquids containing alcohol, like perfume, can ship domestically by ground only. Perishables ship at your own risk and require special packaging plus an extra handling fee.
Shipping to Military Addresses
APO, FPO, and DPO addresses ship at domestic Priority Mail rates, not international, which makes flat rate boxes an efficient way to send care packages overseas. A large flat rate box to a military address costs $30.15 at the counter as of January 2026, slightly less than the standard $31.50.
International Flat Rate Is a Different Service
Priority Mail International Flat Rate has tighter weight limits than domestic. Flat rate envelopes and small flat rate boxes are capped at 4 pounds; medium and large boxes top out at 20 pounds. International shipments also require customs documentation with a specific description, quantity, weight, and value for every item in the package, plus a declared purpose (gift, merchandise, commercial sample). Complete the forms through Click-N-Ship or on paper with PS Form 2976 or 2976-A. Vague descriptions like “household goods” invite delays or seizures at foreign customs.