Which website could you use to look up an unknown zip code?

Using the United States Postal Service's official website, www.usps.gov, is an effective way to look up an unknown zip code. The USPS is the authoritative source for information related to postal services, including zip codes. Their website offers tools specifically designed for locating zip codes, determining address accuracy, and understanding postal regulations.

The USPS not only provides a zip code lookup feature, but also ensures that users have access to the most accurate and up-to-date postal information, which is crucial for mailing and delivery purposes. It's a trusted resource especially for anyone needing to ensure that postal addresses are correct and current.

Other resources may provide zip code information, but the USPS is the definitive source recognized for postal service operations in the United States.