USPS Flat Rate Boxes, Envelopes, and Prices

Published on March 27, 2024
Written by
Filed under Carrier Rates
Read time 7 Minutes

USPS Flat Rate boxes and envelopes allow you to ship up to 70 lbs with USPS Priority Mail® at one low rate to anywhere in the US. The advantage of Flat Rate is that regardless of how much you fit into the packaging, it’s allowable. There are times when USPS Flat Rate boxes are the cheapest way to ship. But, there are also times when standard Priority Mail, or other services, works better. Regardless, knowing how to use Flat Rate shipping options will end up saving you time and money on your shipping.

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What is  USPS Flat Rate 

USPS Flat Rate is a class of packaging that provides specific-sized boxes and envelopes for use with USPS Priority Mail services. They can be shipped anywhere in the US for one flat fee regardless of weight, so long as the parcel weighs fewer than 70 lbs.

How Can I Get Free Boxes From the USPS?

You can visit a USPS facility location or go to the USPS online store to order free USPS-branded flat-rate packaging. These supplies may be free, but it is required that you use them with their intended service. 

When Can I Not Use USPS Priority Flat Rate Boxes?

USPS Flat Rate packaging CANNOT be used with standard Priority Mail services, First Class Mail®, Media Mail®, or with other carriers. They are only allowed for their designated Priority Mail Flat Rate service. If you try to use a Flat Rate box or envelope with a standard Priority service or any other service, the parcel will be returned or a post-billing correction will be sent to your postage account. 

How Much Does USPS Flat Rate Packaging Cost? 

Priority Flat Rate is the USPS’s one-size-fits-all packaging that lets you fit as much as you can into the box as long as it’s under 70 lbs. The prices for Priority Mail Flat Rate and dimensions of each package type are listed below. 

USPS Priority Flat Rate Boxes and Envelopes

USPS Priority Flat Rate Type ShipStation/Commercial Rate Outer Dimensions*Retail Rate**
Flat Rate Envelope$8.0512 1/2″ x 9 1/2″$9.65
Window Flat Rate Envelope$8.0510″ x 5″ or 12 1/2″ x 9 1/2″$9.65
Small Flat Rate Envelope$8.0510” x 6”$9.65
Legal Flat Rate Envelope$8.3015″ x 9 1/2″$9.95
Padded Flat Rate Envelope$8.8012 1/2″ x 9 1/2″$10.40
Small Flat Rate Box$8.558 11/16″ x 5 7/16″ x 1 3/4″$10.20
Medium Flat Rate Box (top-loading)$14.7511 1/4″ x 8 3/4″ x 6″$17.10
Medium Flat Rate Box (side-loading$14.754″ x 12″ x 3 1/2″$17.10
Large Flat Rate Box$19.9012 1/4″ x 12 1/4″ x 6″$22.80
APO/FPO/DPO Large FRB$18.3512 1/4″ x 12 1/4″ x 6″$21.20
*inner dimensions are .25” smaller than outer dimensions
**The rates available through the post office, ShipStation provides discounts on this rate

How Much Do Priority Mail Express Flat Rate Envelopes Cost? 

Currently, the USPS offers a few flat rate options for their USPS Priority Mail Express service. This is a quicker alternative to their Priority Flat Rate offerings—typically being delivered overnight. With a maximum weight of 70 lbs, you can still use their Flat Rate envelope, Legal Flat Rate envelope, or Padded Flat Rate envelope. However, like Regional Rate boxes, the USPS has discontinued their Priority Mail Express Flat Rate Box offerings. 

USPS Priority Mail Express Flat Rate Envelopes

USPS Flat Rate TypeFlat Rate DimensionsFlat Rate PricingFlat Rate Max Weight
Flat Rate Envelope12 ½″ × 9 ½″$24.9070 lbs
Legal Flat Rate Envelope12 ½″ × 9 ½″$25.15 70 lbs
Padded Flat Rate Envelope12 ½″ × 9 ½″$25.3570 lbs
Flat Rate Box Top Loading11 ¼″ × 8 ¾″ × 6″discontinued70 lbs
Flat Rate Box Side Loading12″ × 3 ½″ × 14″discontinued70 lbs

Are USPS Regional Rate Boxes Still Available? 

Effective January 22, 2023, the USPS has discontinued Regional Rate Boxes A and B. While these shorter-distance alternatives to flat-rate boxes are no longer available, you can take advantage of ShipStation’s discounted USPS and UPS rates to make shipping more affordable.  

USPS Priority Mail Package Vs USPS Priority Flat Rate Services

USPS Priority Mail is the standard option for the USPS to send parcels under 70 lbs and do not exceed 108″ in combined length and girth (girth = the distance around its thickest part). These parcels will reach their final delivery in the same timeframe as the flat rate options. However, their prices are structured differently. Whereas flat rate boxes don’t have weight, dimensions, or delivery zone factored into them, standard Priority Mail parcels do. For lighter parcels, it’s usually less expensive to use your own packaging and get a rate. 

Save up to 89% on USPS Rates with ShipStation

ShipStation partners with the world’s most trusted carriers to provide exceptional shipping rates. Whether you’re using Flat Rate or standard packaging, you can save big! These partnerships provide you with a simple way to buy labels and manage multiple shipping accounts with a single source known as ShipStation Carrier Services

ShipStation Carrier Services lets you access savings of up to: 

  • 89% off USPS® retail prices
  • 82% off UPS international service*
  • 77% off UPS® Ground*
  • 73% for UPS 2nd Day Air® service* 
  • 72% for UPS Next Day Air® service*
  • 78% off GlobalPost Economy
  • 75% off DHL Express

*Discounts off UPS daily rates. Rates are limited to shipping from the U.S. only. Rates and any applicable discounts are subject to change at any time without notice.

Written by

James Messer

James Messer is a copywriter specializing in shipping, logistics, and ecommerce.

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