What is the thickness limit for a flat mailpiece?

The thickness limit for a flat mailpiece is indeed .75 inches. This specification is critical for ensuring that mailpieces are eligible for the flat rate mail classification, allowing them to be processed and delivered efficiently. Flats are generally expected to be larger than letter-size mail but must adhere to this maximum thickness to maintain postal system standards. Beyond this limit, mailpieces may be classified differently, impacting postage rates and handling procedures, as they could be treated as parcels instead of flats. Understanding this dimension is crucial for anyone preparing mail for shipment, as it affects not only the cost but also the delivery speed and processing method used by postal services.