Mail Piece Design

The mail piece design information is divided by the shape of the mail piece:


   Post Cards

The dimensions for a post card rate are:


Minimum Dimensions

Maximum Dimensions

First-Class Mail Standard Mail
(Letter Rate)
(perpendicular to the address)
3½ inches 4¼ inches 6 1/8 inches
(parallel to the address)
5 inches 6 inches 11½ inches
Thickness 0.007 inches* 0.016 inches ¼ inch
Aspect Ratio
(length divided by height)
1.3 2.5 2.5

* If 4¼ inches high or 6 inches long, the minimum thickness is 0.009 inches.

In addition, post cards must have:

  • Parallel opposite sides.
  • Square corners are preferred, however finished rounded corners with no more than 1/8 inch radius are acceptable.



The dimensions for a letter are:



Minimum Dimensions

Maximum Dimensions

First-Class Mail Standard Mail
(perpendicular to the address)
3½ inches 6 1/8 inches 6 1/8 inches
(parallel to the address)
5 inches 11½ inches 11½ inches
Thickness 0.007 inches ¼ inch ¼ inch
Weight None 3.5 ounces 3.3 ounces

Nonmachineable Surcharge

If your First-Class Mail letter meets one or more of the following, a 17¢ surcharge is added to each piece:

  • The aspect ratio (length divided by the height) is less than 1.3 or more than 2.5.
  • Is polybagged, polywrapped or enclosed in any plastic material.
  • Has clasps, strings, buttons or similar closure devices.
  • Contains items such as pens, pencils or loose keys or coins that cause the thickness of the mail piece to be uneven.
  • Is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11 inch diameter turn).
  • For pieces more than 4¼ inches high or 6 inches long, the thickness is less than 0.009 inch.
  • Has a delivery address parallel to the shorter dimension of the mail piece.
  • Is a folded self-mailers with the folded edge perpendicular to the address unless the final fold is on the right side (leading edge) and the left edge (trailing edge) and other edges opens are secured with at least one tab or glue line.
  • Is a booklet type piece with the bound edge (spine) along the shorter dimension of the piece or at the top.

Folded Self-Mailers

To be eligible for the automation postage rates, folded self-mailers must be prepared with the folded edge parallel to the longest dimension and the address of the mail piece.  Based on the number of tabs used, these additional standards apply:

  • With one tab, the folded edge must be at the bottom of the self-mailer.  The tab must be placed in the middle of the top edge of the piece.  If formed of a single sheet, the minimum paper basis weight is 28 pounds, if formed of two or more sheets, the minimum is 24 pounds.
  • With two tabs, the folded edge may be at the top or bottom of the self-mailer.  The two tabs must be placed on the open edge.  One tab must be placed within 1 inch of each edge of the mail piece.
  • The self-mailer may have the final fold on the right side (leading edge) of the piece.  The left edge (trailing edge) and the other open edges must be secured by tabs or a glue line.

Reply Mail

The three types of reply mail are:

  • Business Reply Mail – This mail allows the recipient to send mail back to the sender for free with postage and fees collected at delivery from the original sender.  Due to the strict requirements on the design of this mail, Creative Services should design your mail piece.  For more information, please see our Business Reply Mail page.
  • Courtesy Reply Mail – This is a mail piece pre-addressed back to the sender and where the recipient must put postage on the mail piece.  While you may design your own piece, we recommend that you use Creative Services, who can design the pice with the proper bar codes and a box for the postage stamp.
  • Metered Reply Mail – This is a mail piece that has been pre-metered with postage so that the recipient can mail it back at no cost.  Due to the requirement of specific wording that must be printed (not typed or stamped) on the mail piece, Creative Services should design your mail piece.



The dimensions for a flat are: 


Minimum Dimensions*

Maximum Dimensions

First-Class Mail Standard Mail
(perpendicular to the address)
6 1/8 inches 12 inches 12 inches
(parallel to the address)
11½ inches 15 inches 15 inches
Thickness ¼ inch ¾ inch ¾ inch
Weight None 13 ounces Less than 16 ounces

* A flat must exceed at least one of the minimum dimensions.

In addition, a flat must meet these requirements or it is considered a package:

  • A rectangle, a square is considered a rectangle
  • Flexible:
  • Boxes and box-like pieces – with or without hinges, gaps or breaks that allow the piece to bend – are not flats
  • Tight envelopes that are completely filled to form box-like pieces are not flats
  • Uniformly thick:
  • The mail piece cannot have any bumps, protrusions or other irregularties that cause more than a ¼ inch variance in the thickness.  Exclude the outside edges of the mail piece (1 inch from the edge) when determining the variance in thickness.
  • If the contents are signficiantly smaller than the envelope, wrapper or sleeve, mailers must secure those contents to prevent shifting of more than 2 inches within the mail piece.

Rigid Flats

Just marking a flat "Do Not Bend" will not protect the contents. You must include a stiffening material such as fiberboard so that the mail piece cannot be bent.  A rigid flat is considered a package.


The dimensions for a package are: 

  Minimum Dimensions Maximum Dimensions

Length and Girth Combined

(lenght is the longest side

and girth is twice the length

+ twice the thickness)


134 inches - Parcel Post

108 inches - All other classes

Weight ---

First-Class Mail package - 13 ounces

Standard Mail - Less than 16 ounces

Bound Printed Matter - 15 pounds

Priority Mail, Parcel Post, Media Mail, Library Mail - 70 pounds


When preparing packages, please keep the following in mind:

  • Use a corrugated box in good, rigid condition with all flaps intact. Remove or mark out old address labels or other address markings.
  • Protect the contents inside with several inches of packing materials.
  • Close the box securely, use a strong tape 2 inches or more in width. Never use masking or cellophane tape. Use PVC or a filament-reinforced tape.
  • If needed, mark your package "Fragile" or "Perishable" in three places: above the address, below the postage and on the reverse side.
  • Place the address label on the top of the package, which is the most stable orientation of the package as it might ride on a conveyor, do not place the label over a seam or on top of sealing tape.