Mailing Regulations Guide
Below are the requirements for bulk and first-class mail to be acceptable by the U.S. Postal Service. To guarantee your mail will be accepted and to avoid surcharges, be sure your designers follow these regulations.
Bulk Mail IndiciasAspect Ratio for Envelopes
Mail Size and Weight Standards
Window Placement
Bar Code Area
Bulk Mail Indicias
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| Standard Third-Class | Straight First-Class | Presorted First-Class |
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Aspect Ratio for Envelopes
To avoid postal surcharges, the aspect ratio of your mail should conform to the following formula:
Length divided by height = 1.3 to 2.5
Example: a #10 envelope is 9.5 divided by 4.125 = 2.30 A square envelope would have an aspect ratio of 1.0 and is ineligible.
Back to Regulations ListMail Size and Weight Standards
First-Class Mail Size Limits
Mailing pieces .25 thick or less and not meeting the following size requirements are unmailable.
| SHAPE | LENGTH | HEIGHT |
| Postcard | 5 inch minimum | 3 1/2 inch minimum |
| 6 inch maximum | 4 1/4 inch maximum | |
| Letter | 5 inch minimum | 3 1/2 inch minimum |
| 11 1/2 inch maximum | 6 1/8 inch maximum | |
| Large Envelope | 11 1/2 inch minimum | 6 1/8 inch minimum |
| Package | Weight cannot exceed 70 pounds |
Once a piece of mail exceeds the maximum length, height, or thickness of one shape, it automatically gets classified as the next-largest shape.
Unusual Shapes and Sizes
Sometimes a piece of mail requires additional postage because it is a certain shape or size that is difficult to process on mail-sorting machines. These are examples of mail that could require additional postage:
- Square envelopes
- Packages larger than 34 inches long, or 17 inches wide, or 17 inches high
- Envelopes on which the address is written parallel to the shorter edge
- Packages weighing more than 35 pounds
- Books and printed material weighing more than 25 pounds
- Tubes and rolls
Weight and Thickness
Length + girth (distance around the thickest part of the package): Cannot exceed 108 inches
Parcel Post: Cannot exceed 130 inches
Letters: Maximum thickness 1/4 inch
Large Envelopes: Maximum thickness 3/4 inch
Window Placement
Regardless of the size of your envelope, it your addressing shows through a window in the envelope, the window should be placed on your envelope based on the following dimensions:
7/8" from left side of envelope
4 1/2" wide
1 1/8" high
1/2" from bottom of envelope
Bar Code Area
Bar code should be placed as follows:
- Bar code must begin between 4 1/4" and 3 1/2" from the right edge of the envelope
- No higher than 7/16" from bottom of envelope
- No design, artwork or copy can appear between the bar code and the bottom of the envelope
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