Postal Explorer > Publication 51 - International Postal Prices and Fees > Mail Preparation > Size Limits—Priority Mail International
The following size limits apply to Priority Mail International packages sent to most destination countries:
Minimum length and width:
5–1/2 inches by 3–1/2 inches
Maximum length:
42 inches
Maximum length + girth combined:
79 inches
See IMM 230 for the size limits that apply to the country to which you are mailing, or consult your local Post Office.