If you are preparing bulk mail, the very first thing you have to know is what mail size category your mail piece fits into. Not only do these classifications determine postage, they are actually routed differently as they travel across the country, since different mail sorting centers handle different types of mail.

Postage Saver Low-Cost Software for Postal Bulk Mail The four categories are:
postcards;
letters;
flats; and,
parcels

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.

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:
  • are rectangular in shape; and,
  • are at least 3½ inches tall but no more than 4¼ inches tall; and,
  • are at least 5 inches wide but no more than 6 inches wide; and,
  • are at least 0.007 inches thick but no more than 0.016 inches thick.
Postcards get special pricing if you are mailing them at First Class Retail rates or, for bulk mailers, at Presorted First Class rates. First Class Retail postage for a postcard is just 34¢, compared with 47¢ for a letter, with similar discounts in Presorted First Class postcard rates.

But here's the rub. For every mail category other than First Class, postcards are classified as "letters", and don't get any special postcard discount.

That means that if you are sending Standard Class bulk mail, postcards get Standard Class letter pricing. So, if you want to send cards by bulk mail, you don't save any postage by using a small "postcard" instead of, for example, a half-sheet card. (5½ by 8 inches). The larger card will cost you more for paper, but you get much more visibility for the same postage price.

What does the USPS consider to be a letter?

In general, "letters" are any cards or envelopes that:
  • are rectangular in shape; and,
  • are at least 3½ inches tall but no more than 6⅛ inches tall; and,
  • are at least 5 inches wide but no more than 11½ inches wide; and,
  • are at least 0.007 inches thick but no more than ¼ inch thick.
But, here's an exception: small cards that no more than 4¼ inches tall and 6 inches wide and are mailed at First Class Retail or Presorted First Class rates are classified as "postcards" and get a lower postage price.

The exception only applies to First Class prices. For Standard Class bulk mail, and other mail classes, postcards are considered to be "letters" and require the same postage as other pieces in the letters category.

Letters that can be sorted on automated equipment get better postage prices than those which can't. Such pieces are called "machinable" letters. A piece that meets the size requirements above is considered a machinable letter if it also:
  • Weighs no more than 3.3 ounces; AND,

  • Is rectangular (except that letter-sized cards may have rounded corners with a radius of no more than 1/8 inch); AND,

  • Does NOT have any of the following characteristics:

    • Its length divided by its height is less than 1.3 or more than 2.5 (a square piece would have a length divided by height of 1, meaning that square pieces are not machinable); OR,

    • It is polybagged, polywrapped, or enclosed in any plastic material; OR,

    • It has clasps, strings, buttons, or similar closure devices; OR,

    • It contains items such as pens, pencils, or loose keys or coins that cause the thickness of the mailpiece to be uneven; OR,

    • It is too rigid to bend around an 11" diameter turn in the sorting machines; OR,

    • It has a thickness under 0.009 inch, (only applies for pieces at least 4-1/4 inches high or 6 inches long); OR,

    • It has the address running in the same direction as the shorter sides instead of the longer sides; OR,

    • It is a folded self-mailer and has a fold that is perpendicular to the address, unless it meets special USPS folding and sealing requirement for pieces with perpendicular folds; OR

    • It is a booklet and does not meet USPS binding and sealing requirements for booklets.
A letter that is not "machinable" is called "nonmachinable".

For special barcoded (automation) prices, letters must meet additional requirements beyond those for machinable letters. If you are mailing something other than a standard envelope or card, and you want to use barcoded prices, check with your postmaster for eligibility. Barcoded pieces can weigh up to 3.5 ounces.

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 so big that it won't run through automated sorting equipment.

That means that you have a flat if ANY of the following are true:
  • its shorter side is more than 6⅛ inches but not more than 12 inches; or,
  • its longer side is more than 11½ inches but not more than 15 inches; or,
  • it is more ¼ inch thick but not more than ¾ inch thick, (except Periodical Class nonmachinable flats, which may be up to 1¼ inches thick.)
Note that a mail piece is a "flat" if it meets at least one of those requirements. It does not need to meet all of them. So if your piece is larger or thicker in any allowable dimension to be a "letter", and is not larger or thicker than the maximums for flats, it is a flat, even if it fits the other dimensions for a letter.

All flats (except Periodical Class nonmachinable flats) must be flexible enough to go through automated sorting equipment, but not be too "flimsy". There are complicated tests for flexibility and "flimsiness", but in general, a normal card or envelope will be ok.

If you aren't sure whether your piece is flexible or sturdy enough to be a flat, you can see the tests here. Or, just check with your postmaster.

If you're mailing anything in a rigid box, it will not be flexible enough to be a flat, and will be classified as a parcel. But, if you are mailing a CD or DVD, which would normally fail the flexibility test, there are special envelopes that hold the disc in the middle and allows it to be mailed in the letter category.

For barcoded (automation) prices, flats must meet additional requirements. If you are mailing something other than a standard envelope or card, and you want to use barcoded prices, check with your postmaster for eligibility.

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 marketing parcels.

What does the USPS consider to be a machinable parcel?

A machinable parcel is a box that is regular 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.

Parcels can weigh up to 70 pounds, although there are lower limits for various classes of mail. (For example, a Standard Class parcel must weigh less than one pound.)

To be a machinable parcel, the piece must meet ALL of the following:
  • Its length must be at least 6" but not more than 27", AND,
  • Its height must be at least 3" but not more than 17", AND,
  • Its width must be at least ¼" but not more than 17", AND,
  • It must generally weigh at least 6 ounces but not more than 25 pounds.
If the piece is exactly ¼" wide, it must be at least 3½" high.

There are exceptions to the weight limits. Some mailing categories allow machinable parcels up to 35 pounds. And, machinable parcels can weigh less than 6 ounces under the following conditions:
  • A piece weighing 5 ounces or more but less than 6 ounces can be accepted as a machinable parcel if it meets all of the following:
    • Its length must be at least 6" but not more than 12", AND,
    • Its height must be at least 3½" but not more than 9", AND,
    • Its width must be at least ¾" but not more than 6".
  • A piece weighing 3½ ounces or more but less than 5 ounces can be accepted as a machinable parcel if it meets all of the following:
    • Its length must be at least 6" but not more than 7", AND,
    • Its height must be at least 3½" but not more than 5", AND,
    • Its width must be at least 1½" but not more than 3".
Note that there are additional requirements for machinable parcels. If your item is not a "normal" carton, but fits these size requirement, check with your postmaster for the proper category.

What does the USPS consider to be a irregular parcel?

An irregular parcel is pretty much everything that is not a letter, flat, or machinable parcel. The classification includes rolls and tubes up to 26" long, and anything else that is too big or too irregularly shaped to be sorted on automated equipment.

If you have something with a strange shape, or that is larger or heavier than the categories above, check with your postmaster to see if it is an irregular parcel.

What does the USPS consider to be a marketing parcel?

Marketing parcels is a special category that earns lower postage prices when using Standard Class bulk mail, for both commercial and nonprofit Standard Class mailers.

The marketing parcels category is used for 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.



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