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Explaining flat-sized mailpiece rules

Pile of different-shaped packages in postal bin
Do you know a flat-sized mailpiece when you see one?

The Postal Service wants to clear up a few misunderstandings about flat-sized mailpieces.

Here’s what you should know:

• First things first: Know how to recognize flat-sized mailpieces. The Domestic Mail Manual has all the information you need, especially chapters 101 and 201.

Generally speaking, flat-sized mailpieces are no more than 15 inches long, no more than 12 inches high or no more than 3/4 of an inch thick. A flat-sized mailpiece must be rectangular with four square corners, or it must have finished corners that do not exceed a radius of 1/8 of an inch.

Additionally, a flat-sized mailpiece must meet two or three physical characteristic standards, depending on whether the piece is retail-priced or commercial-priced.

Retail flat-sized mailpieces must meet uniform thickness and flexibility standards. Commercial flat-sized mailpieces must also meet deflection standards, in addition to uniform thickness and flexibility.

• A flat-sized mailpiece in a padded or bubble envelope isn’t a parcel. If a mailpiece meets the dimensional criteria and physical characteristics, the piece is considered a flat-sized mailpiece.

The rules spelled out in the Domestic Mail Manual don’t prohibit padded or bubble envelopes from being mailed as flat-sized mailpieces.

• USPS-produced Priority Mail Express Flat Rate Envelopes and Priority Mail Flat Rate Envelopes aren’t flat-sized mailpieces, either. USPS-produced Priority Mail Express Flat Rate Envelopes and Priority Mail Flat Rate Envelopes are flat-priced, not flat-sized.

Determining a thick flat-rate envelope is not eligible for flat-rate pricing is incorrect. Remember: If it fits, it ships (up to 70 pounds domestically, that is).

• More information is available. When in doubt, refer to the Domestic Mail Manual, which is available on the Postal Explorer site, to find the correct answer.

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