What is the maximum size for a flat-sized mailpiece?

The maximum size for a flat-sized mailpiece is 12 inches by 15 inches. This size designation is critical for handling and processing mail within the postal system. Flat-sized mailpieces typically include items such as large envelopes, brochures, and magazines, which can be too large for letter-sized specifications but still need to conform to particular size limits for sorting and delivery efficiencies.

Understanding the size limits helps ensure that mail can be processed through the postal system without delays or issues related to sorting and transport. Anything exceeding the 12 inches by 15 inches limit would fall into another category, which generally requires different handling procedures or additional postage. This highlights the importance of adhering to postal guidelines for size classifications in order to maintain efficient mail processing routes.