USPS Largest Flat Rate Envelope – 2024 Updated

By Phillip Adcock
Last updated: May 2, 2023
USPS Largest Flat Rate Envelope

USPS is widely known as a reliable and convenient delivery service within the States. The company provides diverse services, varying from types of goods, time of delivery, and pricing so that the customers can have the best-customized option based on their budget.

Among USPS’s services, the flat rate envelope is one of the top tiers for its budget-friendly feature. With this combo, you don’t need to care about the weight of the package or the travel distance – the only thing to concern is which envelope size your package fits. 

USPS Flat Rate Envelope Sizes Available 

There are six USPS priority mail envelope sizes available in the meantime. The smallest one is the Priority Mail Small Flat Rate Envelope with 6 * 10 inches (flap closed) dimensions. It is best suited for letters, cards, or small documents.

If your documents cannot fit the previous envelope, try the Priority Mail Flat Rate Envelope – which has a 9.5 * 12.5 inches size. You can put clothes in this envelope, too.So, what if you want an envelope that is as small as the Priority Mail Small but with a see-through cover for easy checking and classifying? No need to worry more; USPS provides the Priority Mail Window Flat Rate Envelope for you. There are two sizes available: 5*10 inches and 9.5*12.5 inches; both have flaps closed and a see-through cover.

In case you want extra padding to protect your package, then it’s better to take a look at the Priority Mail Padded Flat Rate Envelope – which is 9.5 * 12.5 inches big. 

Last but not least, the Priority Mail Legal Flat Rate Envelope with 9.5 * 15 inches is the perfect choice for legal-size documents or for packages that cannot fit the five above options.

What Is The Usps Largest Flat Rate Envelope?

So, after going through 6 USPS priority mail flat rate envelope size choices above, it’s obvious that the Priority Mail Legal Flat Rate Envelope is the USPS’s largest flat rate envelope. We recommend you choose this type because large envelopes can cover and protect your things more effectively than smaller ones. The smaller, the easier to be torn, right?

If you check out the price, the legal flat rate envelope is also budget-friendly. It costs you $9 for a mail with such a big cover, while for other smaller envelopes, the price is 48.7 – not much different, right?


How Much Do Flat Rate Envelopes Cost?

How Much Do Flat Rate Envelopes Cost

As mentioned above, the cost for flat rate envelopes will not depend on the distance or the weight but on the size of the envelopes. There are six types of envelopes, varying from 6*10 inches to 9.5*15 inches. The bigger the envelope is, the more expensive it is. 

Let us list down the cost specifically for you:

  • Priority Mail Small: $9.35
  • Priority Mail: $8.95
  • Priority Mail Window (both small and big sizes): $8.7
  • Priority Mail Padded: $9.3
  • Priority Mail Legal: $9 

You should bring your package to the USPS office and try to fit it into each envelope to see which one is good. Then, see this list to know how much it costs.

When Should I Use A USPS Flat Rate Envelope?

There is one famous saying on the Internet about USPS flat rate service: if it fits, it ships. You can use this delivery option for literally any purpose with any type of mail, from documents to packages. As long as it fits one of the five envelopes, you can use it. 

Compared to other USPS services, the flat rate is much cheaper, so we highly recommend using it as long as possible.

Which Things Can Go In A USPS Flat Rate Envelope?

As mentioned above, “If it fits, it ships”, so you can put anything inside the envelope, as long as it won’t break the envelope, and the mailers can use tapes to enclose it.

However, to protect the system as well as the workers in the delivery service, there are some restrictions that you should notice before putting your things in the envelope. 

We will describe it detailedly in the next section.

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

You had better check the USPS website to see which things are prohibited from going in a USPS flat rate envelope in the meantime because the policies can vary day by day.

Here are some restrictions for USPS flat rate envelopes, based on their latest announcement:

  • Alcohol
  • Alcoholic beverages
  • Hand sanitizer/hand cleanser
  • Lithium batteries
  • Perfume
  • Paint
  • Gasoline
  • Marijuana
  • Explosives
  • Ammunition
  • Airbags

As you can see, most of the prohibited items above are harmful when delivered under strong pressures or hot temperatures. They are likely to explode, cause chemical interaction, or evaporate.

How Many Stamps Do I Need for a Flat Rate Package?

The USPS policy for using stamp postage is quite complicated to break down in a few lines. The most basic approach is accessing the USPS website, finding the postage calculator tool, inputting your package size and services chosen, and then waiting for the tool to work for the final information.

However, if you want to calculate it yourself, let us clarify it here. There is no exact number of stamps for the Flat rate envelope service because the number of stamps will be decided based on the delivery service you choose – the fastest Priority Mail will cost much, then the First-class, the Media, and Retail Ground Mail. So, you should ask the USPS clerk how many stamps you need on your flat rate envelope based on the delivery service you choose.

To learn more about USPS you can also read our articles on:

* Disclaimer: We do not buy, sell or provide service, we only share with you our trusted sources, and experience. In case of any changes in the products or services of the companies, all the information below is supposed to change at any time.

Phillip Adcock is the founder and Managing Director of the research agency Shopping Behaviour Xplained (SBXL), a shopping research organization using psychological consumer insight to explain and help consumers answer their questions about stores and services.

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