Contents Index


C000 General Information

C050 Mail Processing Categories


C050 describes the minimum and maximum size standards for all mail processing categories. The minimum and maximum dimensions for cards, letters, flats, and parcels are described.

1.0 Basic Information

Every mailpiece is assigned to one of the mail processing categories in the following sections. These categories are based on the physical dimensions of the piece, regardless of the placement (orientation) of the delivery address on the piece. Exhibit 1.0 shows the minimum and maximum dimensions for some mail processing categories.

Exhibit 1.0Mail Dimensions

Shows the dimensions for letter-size mail, flat-size mail, and machinable parcels.

2.0 Letter-Size Mail

2.1Minimum and Maximum Size

Letter-size mail is:

a. Not less than 5 inches long, 3-1/2 inches high, and 0.007-inch thick.

b. Not more than 11-1/2 inches long, or more than 6-1/8 inches high, or greater than 1/4-inch thick.

2.2Nonmachinable Criteria

[6-12-03] [4-3-03] A letter-size piece is nonmachinable if it has one or more of the following characteristics (see C010.1.3 to determine the length, height, top, and bottom of a mailpiece):

a. Has an aspect ratio (length divided by height) of less than 1.3 or more than 2.5.

b. Is polybagged, polywrapped, or enclosed in any plastic material.

c. Has clasps, strings, buttons, or similar closure devices.

d. Contains items such as pens, pencils, or loose keys or coins that cause the thickness of the mailpiece to be uneven (see C024.18.0).

e. Is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).

f. For pieces more than 4-1/4 inches high or 6 inches long, the thickness is less than 0.009 inch.

g. Has a delivery address parallel to the shorter dimension of the mailpiece.

h. Self-mailers with a folded edge perpendicular to the address if the piece is not folded and secured according to C810.8.2.

i. Booklet-type pieces with the bound edge (spine) along the shorter dimension of the piece or at the top, regardless of the use of tabs, wafer seals, or other fasteners.

2.3Automation Rates

Letters and cards mailed at automation rates must meet the standards in C810.

3.0 Flat-Size Mail

3.1General Definition

Flat-size mail other than that in 3.2 is (see Exhibit 1.0):

a. More than 11-1/2 inches long, or more than 6-1/8 inches high, or more than 1/4 inch thick.

b. Not more than 15 inches long, or more than 12 inches high, or greater than 3/4 inch thick.

c. Unwrapped, sleeved, wrapped, or enveloped.


For determining automation rate eligibility, automation-compatible flat-size mail is all mail meeting the dimensional criteria in C820.

4.0 Machinable Parcel


A machinable parcel is any piece that is (see Exhibit 1.0):

a. Not less than 6 inches long, 3 inches high, 1/4 inch thick, and 6 ounces in weight. (A mailpiece exactly 1/4 inch thick is subject to the 3 1/2-inch height minimum under C010.)

b. Not more than 34 inches long, or 17 inches high, or 17 inches thick, or 35 pounds in weight. For books or other printed matter, the maximum weight is 25 pounds.

4.2Soft Goods and Enveloped Printed Matter

Soft goods wrapped in paper or plastic bags and enveloped printed matter are machinable only if all packaging standards in C010 are met.


Some parcels may be successfully processed on BMC parcel sorters even though they do not conform to the general machinability criteria in 4.1. A destinating BMC plant manager may authorize a mailer to enter such parcels as machinable parcels rather than as irregular parcels if the parcels are tested on BMC parcel sorters and prove to be machinable. In addition, the following requirements must be met: all mailed pieces must be properly labeled, entered at a post office within the service area of the authorizing BMC, and bear delivery addresses located within the service area of the authorizing BMC.


Items categorized as flats, irregular parcels, or outside parcels may not be prepared as machinable parcels.

5.0 Irregular Parcel (Nonmachinable)

An irregular parcel is a parcel not meeting the dimensional criteria in 4.1. This processing category also includes parcels that cannot be processed by BMC parcel sorters, including rolls and tubes up to 26 inches long; 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.

6.0 Outside Parcel (Nonmachinable)

An outside parcel is a parcel that exceeds the dimensions for machinable parcels. This processing category also includes high-density parcels (other than books and printed matter) weighing more than 15 pounds and exerting more than 60 pounds per square foot (0.4167 pound per square inch) pressure on their smallest side; cartons containing more than 24 ounces of liquid in one or more glass containers; cartons containing 1 gallon or more of liquid in metal or plastic containers; cans, paints; rolls and tubes longer than 26 inches; metal-band strapped boxes, metal boxes, and wood boxes; articles not mailed in boxes or other containers; harmful matter; hazardous materials except ORM-D materials; and containers with all dimensions exceeding the minimum dimensions for a machinable (regular) parcel, if their coefficient of friction or ability to slide on a smooth, hard surface is not similar to that of a domestic-class fiberboard box of the same approximate size and weight.

DMM Issue 58 (8-10-03)