2023 USPS Flat Rate Shipping Guide: Boxes, Envelopes and Pricing

Let’s face it: shipping can get very complicated. There are many variables at play, such as different carriers, service levels, fees and charges. When you add in changing customer expectations and the need to operate at a profit, it’s enough to make your head spin.

USPS flat rate boxes and flat rate envelopes were created to make shipping simple and efficient. They can also provide great value, but it’s important to realize that USPS flat rate shipping is not a one-size-fits-all solution.

This article will explain how it works so that you can make an informed decision around using USPS flat rate shipping for your business. We’ll explore its many benefits, various packaging options, the rates and delivery speeds for USPS flat rate envelopes and boxes, as well as the types of products that are often shipped in flat rate boxes.

What is USPS Priority Mail® Flat Rate?

USPS Priority Mail and Priority Mail Express services provide a simple, economical way to ship packages quickly, to any destination in the U.S. Ultimately, the price is determined by the package you use, not its weight or the distance to its destination. To qualify for Priority Mail flat rates, you must use branded USPS flat rate packaging that is provided free of charge. You can choose from three different envelope sizes and seven various box sizes. 

You pay one flat rate to send a standard-sized package or envelope weighing less than 70 lbs. The delivery will take 1-3 days. USPS flat rate packaging is ideal for shipping small items from coffee mugs to clothing and shoes, computers, basketballs and small appliances. There are even special boxes for shipping board games or sending gifts to service members on military bases.

What are the advantages of USPS flat rate shipping?

There are many good reasons to use USPS flat rate shipping. Advantages include:

  • Easy to use: Flat rate shipping is a no-brainer: there’s no need to weigh or measure every package, and there are no complicated calculations. If an item weighs less than 70 lbs. and fits into a flat rate envelope or box, it ships anywhere in the U.S. for one low price. 
  • Free packaging: You can get flat rate packaging free of charge at your local post office or order online from the Postal Store. USPS flat rate envelopes are offered in packs of 10 and boxes are available in packs or 10 or 25. Forever prepaid boxes and envelopes are also available. Although you’ll still need to purchase tape, peanuts and bubble wrap, the savings of at least one dollar per shipment add up quickly.
  • Predictable costs: No more worries about overspending on shipping. When a customer orders an item, you always know exactly what it costs to ship. 
  • Fast delivery: Your package will arrive in one to three days. Plus, Priority Mail Express includes a money-back guarantee if your parcel doesn’t arrive by the guaranteed delivery date.
  • No surcharges: There are no add-on costs such as fuel surcharges, residential or Saturday delivery surcharges that are common with other services.
  • Deliverability: You can ship to virtually anywhere in the U.S.— including Alaska, Hawaii, Puerto Rico, the U.S. Virgin Islands and Guam—plus Post Office boxes, military bases and embassies.
  • Free tracking and insurance: Tracking and up to $100 in insurance are included at no extra cost.
  • Free pickup: Your mail carrier will pick up your outbound packages at no cost.
  • Security: The USPS is legally authorized to place packages in your mailbox: other carriers cannot. In some cases, USPS may attempt to re-deliver a large package rather than leave it out in the open where it could easily be stolen.
  • Extra services: Extra insurance, proof of mailing, signature confirmation and more are available for an additional fee.
  • Label delivery: No printer? No problem. If in doubt, call your post office or refer to the complete list of restricted items on the USPS web site.

How does USPS flat rate shipping work?

USPS flat rate shipping is easy and convenient. Just follow these simple steps:

  • Step 1. Measure the items you plan to ship to determine whether they can fit into a USPS flat rate envelope or box. The package must close completely without any protrusions or bulges. Verify that the weight does not exceed 70 lbs.
  • Step 2. Obtain a USPS flat rate box or envelope. You must use this packaging to qualify for the flat rate. You can get packaging at your local post office or you can order them online from the Postal Store.
  • Step 3. Place the items to be shipped in the envelope or flat rate box and affix a shipping label with the destination address. 
  • Step 4. Give the package to your mail carrier or bring it to the nearest Post Office for shipment. Or, you can arrange an on-demand pickup for an additional fee.

It’s important to know that USPS does not allow some items, such as cigarettes, perfumes, ammunition or hazardous materials to be shipped by mail. If in doubt, refer to the complete list of restricted items here.

How much do USPS flat rate boxes and envelopes cost?

One of the most attractive features of USPS flat rate shipping is that USPS flat rate boxes and envelopes are provided free of charge. You can easily obtain small quantities from your local post office. For large quantities you can order the USPS flat rate envelopes and boxes you need online from the Postal Store. Online you will have the option to purchase Prepaid Flat Rate Forever packaging, which may be a wise decision if postage rates are expected to increase.

What are the 2023 USPS flat rate box and envelope sizes and prices?

The cost to ship using USPS flat rate boxes and envelopes is very competitive. In contrast to USPS flat rate prices, UPS Simple Rate starts at $10.90 for an extra-small box – but UPS does not have flat rate envelopes or packs, and shippers must provide their own packaging. FedEx One Rate starts at $12.40 for a small box, or $11.10 for a FedEx envelope. FedEx flat rate packaging is free and the company will ship it to you at no cost.

USPS Flat Rate Envelopes      
  Dimensions Priority Mail  Priority Mail Express
Flat rate envelope 12-1/2" x 9-1/2" $9.65 $28.75
Legal flat rate envelope 15" x 9-1/2" $9.95 $28.95
Padded flat rate envelope 12-1/2" x 9-1/2" $10.40 $29.45
USPS Flat Rate Boxes      
  Dimensions Priority Mail  Priority Mail Express
Small flat rate box 8-5/8" x 5-3/8" x 1-5/8" Inside
8-11/16" x 5-7/16" x 1-3/4" Outside
$10.20 NA
Medium flat rate boxes
(top loading or side loading)

11" x 8-1/2" x 5-1/2" Inside
11-1/4" x 8-3/4" x 6" Outside

13-5/8" x 11-7/8" x 3-3/8" Inside
14" x 12" x 3-1/2" Outside

$17.10 NA
Large flat rate box 11-3/4” x 12" x 5-1/2" Inside
12" x 12-1/4" x 6" Outside
$22.80 NA
APO/FPO/DPO flat rate box 11-3/4" x 12" x 5-1/2" Inside
12" x 12-1/4" x 6" Outside
$21.20 NA
Large flat rate board game box 24-1/16″ x 11 7/8″ x 3-1/8″ Outside
23-11/16″ x 11-3/4″ x 3″ Inside
$22.80 NA

How can you prepare to save on shipping and mailing costs in 2023?

While flat rate Priority Mail shipping offers many valuable benefits, it may not always be the fastest or cheapest option. To find the lowest shipping cost for your package, you could visit each carrier’s website, enter your data, then compare all the quotes. You could also use the published rate cards, but it’s difficult to determine the cost of any additional fees or surcharges. Alternatively, you could rate shop all the major carriers at once with Pitney Bowes shipping software. You’ll quickly find the best combination of rates and delivery logistics– and get access to deep discounts that aren’t available anywhere else. Plus, you’ll gain a new level of visibility into all of your shipping and mailing activity, with the ability to set rules to prevent overspending.