What is the minimum length of a letter?

The minimum length of a letter is indeed 5 inches. This specification is part of the standards set by the United States Postal Service (USPS) for determining what constitutes a letter versus other types of mail. The dimensions are defined in such a way to ensure that letters can be processed efficiently through sorting machines and that they meet the requirements for delivery.

In the context of postal regulations, letters must also adhere to other dimensional requirements regarding height and thickness, but the minimum length specifically sets a foundational guideline that helps categorize mail appropriately. Understanding these standards is crucial for anyone handling postal services, as it helps ensure the smooth processing and delivery of mail.