What Is A Flat USPS? (All You Need To Know)

The United States Postal Service can ship it all, big or small, whether it fits in an envelope or weighs 70 pounds and has to be double-reinforced with lots of packing tape.

Everyone is familiar with all the different types of boxes USPS ships, including its famous Flat Rate boxes.

But what about Flats? What is a Flat USPS can ship? What constitutes a Flat? I have the answer you seek!

What Is A Flat USPS In 2024?

The United States Postal Services considers large envelopes, newsletters, and magazines to be Flats as of 2024. Flats are larger than a standard letter envelope but not big enough to be a parcel. Flats must conform to size standards, particularly thickness; some mail classes include Flat Rate Flats in their services.

To learn more about what is considered a Flat, the maximum dimensions, the difference between a Flat and a parcel, and the difference between a Flat and a letter, keep reading!

What Is Considered A Flat With USPS?

For something to be considered a Flat, it must meet both minimum and maximum measurements.

For example, the height must be more than 6 and 1/8 inches but cannot be more than 12 inches. Also, the length must be at least 11 and ½ inches but cannot be more than 15.

Also, the thickness must measure at least ¼ of an inch but no more than ¾ of an inch. Finally, the weight must be no more than 13 ounces.

Think of manila envelopes, a newsletter from your local animal shelter, the latest issue of Vogue magazine, and so on.

Moreover, Flats are popular among businesses, such as attorneys’ or medical offices, where bills or sensitive documents must be mailed out without being folded or creased.

Additionally, some popular mail classes that ship Flats include First-Class, which has a base rate of up to one ounce, then costs an extra $0.20 per additional ounce.

With that, USPS carries Flat Rate envelopes that qualify as Flats, including its basic Flat Rate envelope, Legal Flat Rate, and Padded Flat Rate.

So, as long as the weight doesn’t exceed 13 ounces, these are covered under the definition of a Flat.

Finally, these are available for Priority Mail (fast shipping) and Priority Mail Express (the fastest USPS offers domestically).

How Much Postage Do You Need To Mail A Flat USPS?

Postage for Flats being shipped via First-Class are calculated by weight.

For example, Flats weighing up to one ounce require just $1.16 in postage to mail domestically. After that, the cost is an additional $0.20 per ounce.

However, if you want a faster service, you can send a Flat Rate envelope, which qualifies as a Flat, for just $8.95.

Also, if you want guaranteed next-day or two-day delivery, you could send a Flat Rate envelope via Priority Mail Express; just expect to pay $26.95 for the Flat Rate envelope.

What Is The Difference Between A Flat And A Parcel?

What Is The Difference Between A Flat And A Parcel?

One difference between a Flat and a parcel is size. Flats are, by definition, quite limited; their width, for example, cannot be any greater than 3/4ths of an inch.

On the other hand, parcels are larger, box-like, whether square or rectangular. Moreover, another difference is price.

For example, Flats are cheaper to ship than parcels, starting at just $1.16 for First-Class Flats.

Finally, Flats must be much lighter than parcels, as the maximum weight is 13 ounces. In contrast, many parcel shipping classes for USPS allow up to 70 pounds.

Is A Padded Envelope Considered A Flat?

As long as the padded envelope meets the size and weight requirements, a padded envelope could certainly be considered a Flat by the Postal Service.

That said, USPS sells Flat Rate padded envelopes via its Priority Mail and Priority Mail Express shipping classes.

What Is The Difference Between Flat And Letter USPS?

A Flat and a letter have different definitions under the United States Postal Service.

For example, the definition of a Flat is restricted by specific height, length, width, and weight dimensions, and there is no overlap between Flats and letters.

Moreover, letters fit in standard or business-size envelopes, are not more than 3.5 ounces and can be sent with just $0.58 worth of postage.

In contrast, Flats start at $1.16 and increase in increments of $0.20 for every additional ounce, up to 13 ounces.

To know more, you can also read our posts on USPS Flat rate envelope restrictions, how fast is USPS flat rate shipping, and does USPS buy back unused stamps.


USPS Flats refer to a type of mail with particular dimensions, the most important of which is the width, which cannot exceed 3/4 of an inch, and weight, which cannot exceed 13 ounces.

Also, popular types of Flats include legal envelopes and manila envelopes or magazines, and other printed publications from different organizations.

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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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