If your mailpiece isn’t a card[1], letter[2], or a flat (large envelope[3]), then it’s a parcel. You may be surprised to find out that "parcels" are not just big boxes. Many mailers send small parcels in all classes of mail. Parcels offer some of the best value for your postage dollars.

All parcels fall into one of two categories: machinable and nonmachinable. These categories are determined by size and weight.

Machinable Parcels

"Machinable" parcels fit through the Postal Service’s automated parcel sorting machines. They must measure:

• At least 3 inches high x 6 inches long x ¼ inch thick, and at least 6 ounces.
• No more than 17 inches high x 34 inches long x 17 inches thick, and no more than 35 pounds (25 pounds for books or other printed matter).

Machinable parcels are less expensive to mail than nonmachinable parcels (which get charged a surcharge) and are processed and delivered more efficiently.

More about Physical Standards for Discount Parcels[4]

More about Discount Parcels - Parcel Post[5]

Nonmachinable Parcels

Nonmachinable parcels have at least one dimension (including weight) that exceeds the limits for a machinable parcel. Other parcels are nonmachinable based on content, weight, or other physical characteristics.

Nonmachinable parcels are more difficult and costly for the Postal Service to process and deliver. To cover those extra costs, there is a surcharge for nonmachinable parcels.

Balloon and Oversized Rates for Parcels

Some parcels may be subject to specialized rates. Priority Mail (zones 1-4) and Parcel Post parcels that are large but very light (less than 20 pounds) get charged the rate for a 20 pound package. This is often referred to as a balloon rate. Very large Parcel Post parcels (over 108 inches but not more than 130 inches in combined length and girth) get charged an oversized rate.

Sizes for cards[6]

Sizes for letters[7]

Sizes for flats[8]