Mailing Standards of the United States Postal Service, International Mail Manual> 2 Conditions for Mailing > 230 Priority Mail International
Priority Mail International service is considered a parcel stream for mail exchange purposes.
The maximum weight for items mailed using Flat Rate Envelopes and Small Flat Rate Priced Boxes is 4 pounds.
The weight limit for items mailed using the Medium and Large Flat Rate Boxes is 20 pounds.
The maximum weight limit for Priority Mail International service is 70 pounds, but lower country-specific weight limits might apply. To determine the maximum weight limit for each country, see the Individual Country Listings.
The minimum and maximum dimensions for Priority Mail International parcels are as follows:
For all parcels, length is the longest side of the parcel, and girth is the measurement around the thickest part that is perpendicular to the length. The following examples can assist mailers in determining length or length and girth combined for rectangular and nonrectangular parcels. See Exhibit 231.23.
Measuring Parcel Dimensions