USPS Guidelines For Flat Size Mailpieces

Designing for Automation Flats!

Last week we discussed designing letters and postcards for automation postage rates.  Below are guidelines for producing flat size mailpieces.

But first! What is the upside to creating automatable mailpieces?

Automation Benefits:

  • Greater postage discount
  • Faster mail processing
  • Better, more consistent service

A flat is described as a rectangular and smooth piece of mail that is too big in at least one direction to be a letter.  The length of a flat size mailpiece is the longest dimension.  The height is the dimension perpendicular to the length.

Flats qualify for automation prices if they meet specific addressing, barcoding and design standards.  Remember that beginning January 28, 2013 your maipiece must use an Intelligent Mail Barcode to be eligible for automation postage discounts.

Designing for Automation Flats:

  • Physical Characteristics
    • Minimum height is 5”
    • Maximum height is 12”
    • Minimum length is 6”
    • Maximum length is 15”
    • Minimum thickness is .009”
    • Maximum thickness ¾”
    • Weight limits
      • First Class not more than 13 ounces
      • Standard less than 16 ounces
  • In addition
    • Must meet specific flexibility standards
    • Must be uniformly thick so that any bumps, protrusions, or irregularities do not cause more than ¼” variance in thickness.
    • Must be rectangular in shape
  • Barcode Standards
    • Must be at least 1/8” from any edge on the address side of the mailpiece
    • Minimum clearance between the barcode and any information line above or below it within the address block must be at least 0.040” for POSTNET and 0.028” for an IMb (IMb is mandatory beginning January 28, 2012)
    • Window Envelopes and Address Labels
      • Minimum clearance between printing and any left or right edge of the window must be 1/8”
      • Minimum clearance between printing and top or bottom of the window must be 1/25”
  • Address Standards
    • Must be within top half of mailpiece
    • A vertical address may cross midpoint if it begins or ends within 1” of top edge (important for small flats)
    • Must be on same side as postage
    • Flats using the Intelligent Mail barcode may use 6 point type for address if it is printing in all capital letters
    • If  there is no Intelligent Mail barcode, minimum type size is 8 point.
  • Address Format

Sue Sample

ABC Company

123 Main Street

Anytown, MO  ZIP+4

  • Address Tap Test (address readability through envelope window)
    • Mail using a window envelope must show complete address, with 1/8” clearance at top, bottom and both sides of window
    • Test address placement with two taps on bottom and two taps on each end – address should remain within window with 1/8” clear space
  • Print Contrast
    • Preference is dark type on light paper
    • Recommend light pastels or neutrals
    • Avoid dark, bright or black papers
    • Avoid dark fibers
    • Avoid bleed through

What steps will you take today to ensure your mail is automation compatible? Don’t lose out on reduced postage rates for automation mail!

If you have questions or need more information, please contact one of Strahm’s Customer Service Representatives.  They can be reached at or (816) 756-2733.


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