SIZE STANDARDS

Minimum Sizes
Pieces 1/4 of an inch or less in thickness are mailable provided they are:
    1.  Rectangular in shape.
    2.  At least 3 1/2 inches high.
    3.  At elast 5 inches long (items sent to foreign countries must be at least 5 1/2 inches in length).
    4.  At least .007 of an inch thick (about the thickness of a postal card).
Mail not meeting these minimums will be returned to the sender.

Nonstandard-Size Mail
First Class Mail or single piece Third Class mail weighing one ounce or less is nonstandard if it exceeds any of the following size limits:
    1.  Its height exceeds 6 1/8 inches, or
    2.  Its length exceeds 11 1/2 inches, or
    3.  Its thickness exceeds 1/4 of an inch, or
    4.  Its length divided by its height is less than 1.3 or more than 2.5 inches.
The same criteria apply to international letters and regular printed items weighing one ounce or less. Nonstandard surcharge is 10¢ added to the regular postage rate.

Maximum Size    
This is 108 inches, length plus girth.  A simple way to explain this measurement is to use a person as an example:  
    1.  Measure the person's height,
    2.  Measure the waist or greatest point of girth, 
    3.  Add together.
If after adding the length and girth together the total is 108 inches or less, the parcel is mailable.