What is the maximum variance in thickness allowed for a flat mail-piece?

The maximum variance in thickness allowed for a flat mail-piece is 1/4 inch. This standard is in place to ensure proper handling and processing of mail within the postal system, as variations in thickness can affect how mail is sorted and delivered. A variance of 1/4 inch is considered acceptable because it maintains the integrity of the mail stream and minimizes disruptions in automated processing equipment.

Thicker or thinner mail may not meet postal guidelines, which can result in delays or additional postage fees. Ensuring compliance with this thickness standard helps to ensure that all mail is treated consistently and efficiently within the postal system.