If your mailpiece isn’t a postcard[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.

Parcels Dimensions

Generally, commerical parcels must measure:

• At least 3 inches high x 6 inches long x 1/4 inch thick.
• Except for Parcel Post and Parcel Select, no mailpiece may measure more than 108 inches in length and girth combined. Length is the measurement of the longest dimension and girth is the distance around the thickest part (perpendicular to the length). Maximum weight is 70 pounds.

Machinable Parcels

• No more than 27 inches long x 17 inches width x 17 inches high.
• No more than 25 pounds (35 pounds for Parcel Select and Parcel Return Service, except books and other printed matter which cannot exceed 25 pounds).

More about Physical Standards for Commercial Parcels[4]

More about Commercial Parcels - Parcel Select[5]

Balloon and Oversized Prices for Parcels

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

Sizes for postcards[6]

Sizes for letters[7]

Sizes for flats[8]