What is the minimum thickness for a letter?

The minimum thickness for a letter is 0.007 inches. This measurement is important because it establishes the threshold for what qualifies as a letter for postal purposes. If a letter is thinner than this minimum thickness, it may be classified differently, leading to potential changes in postage rates or processing methods. Understanding this standard helps ensure that mailing requirements are met, thereby reducing delays or additional charges when sending letters through the USPS. In contrast, other thickness options do not meet the established minimum, making them unqualified as standard letters in postal terms.