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Quick Guide To Measure Mailing Letters - Private PO Mailbox Rental Honolulu Back to the top

Quick Guide To Measure Mailing Letters

Here are some quick measurements on acceptable mailing sizes when mailing letters via the United States Postal Service.

  • Maximum size for Letters: 11-1/2" long x 6-1/8" high
  • Maximum thickness for Letters: 1/4" thick
  • Minimum size for Postcards and Letters (any size smaller that these dimensions cannot be mailed): 5" long x 3-1/2" high
  • Maximum size for Postcards: 6" long x 4-1/4" high
  • Maximum thickness for Large Envelopes: 3/4" thick

Once a piece of mail exceeds the maximum length, height, or thickness of one shape, it automatically gets classified as the next largest shape and it's equivalent postage.

Also, large envelope prices will be applied to letter-sized items over 3.5 ounces.

To double check or get an estimate on the cost of your postage, visit the United States Postal Service website linked here:

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