USPS Flat Rate Envelope Restrictions (Your Full Guide)

One of USPS’ most popular mail products is the Priority Mail Flat Rate Envelope. These envelopes (which come in 7 different sizes) feature one low flat rate.

That means the price you pay is determined by the box or envelope you choose, not by the weight or distance the package is traveling.

As a result, they can help you save a lot of money. If you want to know more about how to use Flat Rate Envelopes, then this is the article for you.

USPS Flat Rate Envelope Restrictions In 2022

USPS Flat Rate Envelopes feature one low flat rate. Postage price is determined by the envelope type, rather than the weight or distance the package is traveling. Additionally, flat Rate envelopes are usually the most inexpensive shipping option available. To benefit from Flat Rate pricing, envelopes must weigh less than 70 lbs. and have a maximum dimension of 108 inches.

If you’d like to know more about which types of envelopes are available, how much you can expect to pay and which items can ship in Flat Rate envelopes, then keep reading!

What Types Of Flat Rate Envelopes Are Available?

USPS offers a variety of different envelope sizes as part of their flat rate envelope service. Check out the table below to see the different envelope types, envelope dimensions and some suggested uses.

Envelope Type Dimensions Suited For
Priority Mail Small Flat Rate Envelope 10 inches x 6 inches (with the flap closed) Letters, cards and small documents like passports.
Priority Mail Flat Rate Envelope 12.5 inches x 9.5 inches (with the flap closed) Documents, clothes
Priority Mail Window Flat Rate Envelope (Small) 10 inches x 5 inches (with the flap closed) Letters and other small documents like passports.
Priority Mail Window Flat Rate Envelope (large) 12.5 inches x 9.5 inches (with the flap closed) Full-page documents and large pre-addressed envelopes.
Priority Mail Padded Flat Rate Envelope 12.5 inches by 9.5 inches (with the flap closed) Any items that need extra padding, manila envelopes
Priority Mail Legal Flat Rate Envelope 15 inches x 9.5 inches (with the flap closed) Legal size documents

How Much Do Flat Rate Envelopes Cost?

Here is a breakdown of Flat Rate envelope postage:

Envelope Type Price
Priority Mail Small Flat Rate Envelope $8.70
Priority Mail Flat Rate Envelope $8.70
Priority Mail Window Flat Rate Envelope (both sizes) $8.70
Priority Mail Padded Flat Rate Envelope $9.30
Priority Mail Legal Flat Rate Envelope $9.00

Keep in mind that the prices above reflect the postage price. Envelopes are free of charge.

You can pick up a supply of free Flat Rate envelopes the next time you go to the post office or you can order them online via USPS’ website.

How Do I Attach Postage To A Flat Rate Envelope? 

How Do I Attach Postage To A Flat Rate Envelope?  USPS

You have several options when it comes to purchasing and using postage on a Flat Rate envelope.

You can use a combination of stamps equaling the postage price, you can use the Click-N-Ship service to buy and print postage at home, or you can affix a prepaid label from a company like eBay or Poshmark.

When Should I Use A USPS Flat Rate Envelope?

USPS Flat Rate Envelopes are almost always the cheapest shipping option, however there are some exceptions.

You should use your own envelope when mailing things that are exactly 1 lb. and traveling locally.

Similarly, you should use your own envelope if what you’re sending weighs less than 1 lb. then ship using the USPS First-Class Package Service.

What Are The Maximum Dimensions For A Flat Rate Envelope?

Maximum dimensions are the same for all Flat Rate products (envelopes and boxes).

These products should have a maximum combined length and girth (girth being the distance around the widest part) of 108 inches.

While you won’t get anywhere near the maximum dimensions with a Flat Rate Envelope, it is important to keep in mind that the envelope flaps and seals must be able to close within normal folds.

If your envelope is so full that you have to use an excessive amount of tape to close it, USPS will charge you according to the weight of the envelope and the zone you’re mailing to. In other words, Flat Rate pricing won’t apply.

Maximum weight for Flat Rate Envelopes is 70 lbs. domestically and 4 lbs. internationally.

What Can Go In A USPS Flat Rate Envelope?

As the USPS saying goes “if it fits, it ships.” That means you can put just about anything in the envelope without stretching it or using excessive tape to close it. Bulges in the envelope are acceptable.

Documents are an obvious choice to put in Flat Rate Envelopes, but you can also put clothes, shoes or toys.

What Can’t Go In A USPS Flat Rate Envelope?

As with any piece of mail that passes through the USPS mail system, there are prohibited and restricted items for Flat Rate Envelopes.

Below is a list of some common examples of prohibited and restricted items. Please be aware that this list is non-exhaustive.

If you have doubts or questions about an item you’re mailing, check out the USPS website for more details.

Here are some prohibited items: 

  • Air bags
  • Ammunition
  • Explosives
  • Gasoline
  • Marijuana (medical or otherwise)

Here are some restricted items:

  • Alcoholic beverages
  • Hand sanitizer
  • Lithium batteries
  • Paint
  • Perfume

Again, check out the USPS website for more details about how to mail restricted items.

To find out more, you can also see our posts on USPS shipping restrictions, shipping shoes at USPS, and shipping jewelry at USPS.

Conclusion

USPS’ Flat Rate envelopes are a quick, convenient and cost effective way to ship documents, clothing, toys or whatever else you need to send. Thanks to the 7 envelope sizes, every USPS customer will find the Flat Rate envelope perfect for their item.

What’s more, the rules for using Flat Rate envelopes are fairly flexible. As long as your envelope weighs less than 70 lbs., has maximum dimensions of 108 inches, closes on its own and doesn’t contain prohibited items, then the sky’s the limit for what you can mail.

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Marques Thomas

Marques Thomas graduated with a MBA in 2011. Since then, Marques has worked in the retail and consumer service industry as a manager, advisor, and marketer. Marques is also the head writer and founder of QuerySprout.com.

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