What Is USPS Flat Rate Envelope? (All You Need to Know)

When sending documents, books, or anything flat, you might choose to eschew encasing it in an entire box and instead opt for an envelope.

Luckily, with the United States Postal Service, you can choose from a variety of envelopes, most of them Flat Rates. But what is a USPS Flat Rate envelope, and how many different kinds are there? I’ve got the answer you seek, so keep reading!

What Is a USPS Flat Rate Envelope In [currentyear]?

USPS Flat Rate Envelopes are special mailers that can be obtained for free, and ship to any destination in the U.S. and its territories for a singular low price in [currentyear]. The cost to ship a Priority Mail Flat Rate envelope is $8.95. There are currently nine different types of Flat Rate envelopes to choose from.

To learn more about what you can mail in a Flat Rate envelope, where you can obtain them and how much they cost, what the price is to mail one, and even where you can mail them from, keep going!

What Can You Mail in a Flat Rate Envelope?

The obvious item to send in a Flat Rate envelope is a document, whether that be a manuscript, a term paper, or even a letter that you’d rather reach its destination sooner, versus later.

(First-Class mail can take up to 10 days, after all.)

However, people can get away with sending other items, like books or journals, or even small boxes, using this Flat Rate envelope hack.

The rules for shipping in a Flat Rate envelope are as follows:

  • “If it fits, it ships”: As long as you can close the envelope using the provided adhesive strip, you’re good to go.

However you have to make it fit, so if the item is in there and the top flap closes, you can ship the item.

If the top flap does not close easily, though, and requires the aid of tape or other adhesives, you’ll likely have to bump up to a Flat Rate box.

  • You can use tape, but only to secure the seams of the envelope – not to hold it closed.

Frankly, if your envelope would burst open without tape, you’re better off moving up to a Flat Rate box.

  • Flat Rate is about price: The “Flat” in Flat Rate is referring to the price – which is the same, no matter where the item is heading or how much it weighs (under 70 lbs.).

However, this doesn’t mean that the envelope has to be flat! Again, if you can make your items fit and get them closed using the adhesive strip, that’s all you need to ship.

Are USPS Flat Rate Envelopes Free?

Happily, USPS Flat Rate envelopes are free!

You can pick them up at your local Post Office location, and some lobbies are open 24/7, so you can access them any time of the day or night (use this handy locator before you go).

As well, you can order them online and have them shipped to you, completely for free.

Using the Postal Store, you can order envelopes in sets of 10 (so if you just want one, you’re better off making the trek to the Post Office).

Once you place your order, your mail carrier will bring the envelopes during their next delivery loop and leave them at your front door- easy peasy!

Can You Use Your Own Envelope for Flat Rate?

Can You Use Your Own Envelope for Flat Rate? USPS

You cannot use your own envelope for USPS Flat Rate shipping, as that would defeat the purpose.

Instead, the Postal Service makes its Flat Rate envelopes easily accessible, through your local Post Office or online, where they are completely free.

How Much Does It Cost to Ship a Flat Rate Envelope?

A USPS Priority Mail Flat Rate envelope is very affordable; envelopes 12.5” x 9.5” or smaller cost just $8.95 to ship, anywhere in the U.S. and territories.

A Legal Flat Rate envelope costs $9.25, while a Padded Flat Rate envelope costs just $9.65.

However, USPS Priority Mail Express Flat Rate envelopes are a bit more expensive, at $26.95 for a regular, $27.10 for a Legal, and $27.50 for a Padded one.

But then, you are paying for overnight or two-day shipping, which certainly accounts for the added cost.

How Much Does It Cost to Ship a Padded Flat Rate Envelope?

The cost to ship a Priority Mail Padded Flat Rate envelope via USPS is just $9.65, while a Priority Mail Express Flat Rate Padded Flat Rate envelope costs $27.50 to ship.

Like all Flat Rate envelopes, you don’t have to keep the envelope flat to mail it.

Rather, as long as it closes easily along the adhesive strip provided, you can make the envelope into whatever shape you have to, plus have the additional security of padding!

Can You Drop a Flat Rate Envelope in a Mailbox?

If you haven’t yet paid your postage, you can head to the Post Office and a worker will take your information (as well as your recipient’s) and print a label for you.

Afterward, they’ll usually just take it over the counter and put your envelope with the rest of the day’s outgoing mail.

As well, you can print your label at home and affix it yourself. At that point, you can drop it into any mailbox you like, starting with your own.

Additionally, if you’re out running errands and see a Big Blue Box, you can drop it in there, too!

Is a Priority Mailing Envelope the Same as a Flat Rate Envelope?

A USPS Priority Mailing envelope isn’t the same as a USPS Flat Rate envelope.

In fact, a regular USPS Priority Mail envelope doesn’t say Flat Rate on it, and therefore will not be eligible for Flat Rate pricing.

Rather, all Flat Rate envelopes will say “Flat Rate” on them, to signify their mail class.

To learn more, you can also read our posts on USPS Flat Rate, USPS Flat Rate envelope restrictions, and what is a Flat USPS.


A USPS Flat Rate envelope is the perfect low-cost shipping solution for flat items, like documents, books, or small boxes.

As long as the lip of the envelope closes easily and the adhesive on the envelope keeps it closed on its own, you can ship using Flat Rate and save potentially hundreds.

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Mackenzie Jerks

Mackenzie is a freelance writer and editor, published author, and music enthusiast who holds a Bachelor of Science in Business Administration. When she’s not writing, Mackenzie is either wrapped up in a book, discovering new music, or introducing herself to a new fitness regimen.

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