Is it a Postcard, a Letter, a Flat or a Parcel?

Scott HochbergScott Hochberg

These are the four main size categories that USPS uses to classify mail and determine postage. Is your mail a postcard, letter, flat or parcel? Here's the quick answer:
(Click on the links for more detailed information.)

A postcard is a card (not an envelope) that fits ALL THREE of the following:
A letter is a rectangular card or envelope that fits ALL THREE of the following:
A flat is a rectangular card or envelope that is larger or heavier than a letter, meeting AT LEAST ONE of the following:
AND, meeting ALL of the following: To be classified as a flat, a mail piece must also:
A parcel is an envelope, carton, tube, or anything else that fits ANY one of the following:
Read on if you need more details on postcards, letters, flats and parcels.
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What are the USPS size categories for bulk mail?

If you are preparing bulk mail, the very first thing you have to know is what mail size category your mail piece fits into. There are four basic size categories: postcards, letters, flats and parcels.

There are different postage rates for mail in each size category. For bulk mail, the size category also determines how you will sort the mailing, since different mail sorting centers handle different types of mail.

Unfortunately, the terms used for each of these categories are confusing. For example, sometimes when you mail a "letter", the postal service classifies it as a "flat", while sometimes when you mail a flat card, the postal service classifies is as a "letter".

The basic rule to remember is that these categories are based on the size of the piece, not the content.

Our Postage $aver bulk mail preparation software automatically determines the correct sorting and postage for the category of mail you are sending.

Here's what the rest of this page covers:
red dotWhat are postcards?
red dotWhat are letters?
red dotWhat makes a letter machinable vs. nonmachinable?
red dotWhat are flats?
red dotWhat are parcels (including machinable, irregular and nonmachinable parcels)?
red dotWhat are marketing parcels?

What does the USPS consider to be a postcard?

While most people consider any card that goes through the mail to be a "postcard", that's not the USPS definition. The only cards that are actually classified by USPS as "postcards" are cards (not envelopes) that: Postcards get special pricing if you are mailing them at First Class retail (regular mail) rates or at Presorted First Class rates. First Class retail postage for a postcard is just 36¢, compared with 55¢ for a letter, with similar discounts in Presorted First Class postcard rates.

But for every mail category other than First Class retail and Presorted First Class, postcards are classified as "letters", and don't get any special postcard discount.

That means that if you are sending Marketing Mail bulk mail, postcards get Marketing Mail letter pricing.

If you want to send cards by Marketing Mail bulk mail, you don't save any postage by using a small "postcard" instead of a larger piece (for example, a half-sheet card). The larger card will give you much more visibility for the same postage rate.

What does the USPS consider to be a letter?

In general, "letters" are any cards or envelopes that: Here's an exception: small cards that no more than 4¼ inches tall and 6 inches wide and are mailed at First Class retail (regular mail) or Presorted First Class rates are classified as "postcards" and get a lower postage rate.

But for Marketing Mail bulk mail and other mail classes, small cards are classified as letters and require the same postage as other pieces in the letters category. That means that for Marketing Mail, there is no postage advantage to sending the small postcards instead of larger cards (5½" x 8½", for example), and larger cards are more likely to be noticed by the recipient.

What makes a letter machinable vs. nonmachinable?

A surcharge is added to your postage rate if your letter-sized mail cannot be sorted on automated equipment. Letters that cannot be sorted on automated equipment are called "nonmachinable letters", and those that can are called "machinable letters".

Normal letter-sized mail is classified as "machinable", and there is no surcharge.

Probably the most common way that a letter becomes nonmachinable is to have an unusual shape. Anything that's not rectangular is nonmachinable. And, a rectangle that is vertical, square, or too narrow is nonmachinable.

To check the shape of your letter, divide the length of the piece by its height. If the result is less than 1.3, or more than 2.5, the piece is nonmachinable.

For example, for a 6" x 6" square card, divide 6/6, which is 1. Since 1 is less than 1.3, a square card is nonmachinable.

For a long narrow piece that is 11" long by 4" high, divide 11/4, which is 2.75. Since 2.75 is more than 2.5, the piece is nonmachinable.

Here are all the circumstances that make a letter nonmachinable. A letter is nonmachinable if it has ANY of the following characteristics:
There are specific details for many of these conditions. Contact us or your postmaster if you need further details.

Also, there is a separate set of restrictions for envelopes carrying a CD or DVD. We can provide those details as can your postmaster.

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What does the USPS consider to be a flat?

A flat is a mail piece that is too big in at least one direction to be a letter, but not too big.

That means it must meet AT LEAST ONE of the following:
AND, meet ALL of the following: All flats (except Periodical Class nonmachinable flats) must be flexible enough to go through automated sorting equipment, but not be too "flimsy" (which is called "deflection"). There are complicated tests for flexibility and deflection, but in general, a normal card or envelope will be ok.

If you're mailing anything in a box, it will not be flexible enough to be a flat, and will be classified as a parcel.

What does the USPS consider to be a parcel?

A parcel is anything that is too large or rigid to be a flat.

Parcels are divided into three categories, as described below: machinable parcels, irregular parcels, and nonmachinable parcels. There is also a special category called Marketing Mail Marketing Parcels, which can be either machinable or irregular.

A machinable parcel is a box that is rectangular in shape (not including tubes, rolls, etc.) so that it could be processed on automated sorting equipment, and that is too large or rigid to be a flat. Soft goods wrapped in paper or plastic bags, and enveloped printed matter, can be machinable under certain conditions. Check with your postmaster.

To be a machinable parcel, the piece must meet ALL of the following: A piece that is exactly ¼" thick must be at least 3½" high.

A parcel weighing 5 ounces or more but less than 6 ounces, must meet the following more restrictive requirements to be machinable: A parcel weighing 3½ ounces or more but less than 5 ounces, must meet the following more restrictive requirements to be machinable: An irregular parcel is pretty much everything that is not a letter, flat, or machinable parcel, as long as it is not larger than 27" x 17" x 17" in any dimension.

Irregular parcels include rolls and tubes up to 26" long.

And, irregular parcels include merchandise samples that are not individually addressed and are not letter-size or flat-size; unwrapped, paper-wrapped, or sleeve-wrapped articles that are not letter-size or flat-size; and articles enclosed in envelopes that are not letter-size, flat-size, or machinable parcels.

A nonmachinable parcel is anything that is too large, in any dimension, or too heavy to be a machinable parcel or an irregular parcel. It also includes parcels that are particularly heavy for their size (other than printed matter), cartons containing large amounts of liquids, items not packed in cartons (like cans, metal boxes, etc.), and other unusual containers or hazardous materials.

A roll or tube longer than 26" is also a nonmachinable parcel.

Nonmachinable parcels cannot weigh more than 70 pounds, and may not measure more than 130" in length and girth combined.

Parcels that do not fit either the machinable, irregular or nonmachinable categories cannot be mailed using USPS. Specific classes of mail (Marketing Mail parcels, for example) have much more restrictive size and weight limits. Always check the size, weight and shape restrictions for the class of mail you want to use.
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What is a Marketing Parcel?

A marketing parcel is a machinable or irregular parcel sent using Marketing Mail bulk parcel service that contains product samples or other promotional items that are sent out in bulk. The purpose of the mailing must be to encourage recipients to purchase a product or service, make a contribution, support a cause, form a belief or opinion, take an action, or provide information to recipients. It cannot be used for shipping merchandise that customers have ordered.

Marketing parcels are required to be addressed using an "alternative" addressing format ("OCCUPANT", or the person's name plus "OR CURRENT OCCUPANT", etc.).

Marketing parcels have a maximum size of 12" by 9" by 2". If the parcel is ¼" thick or less, it must be at least 3½" wide by 5" long.

For more information about Marketing Mail Marketing Parcels, see our bulk parcels guide.