To find your ZIP code extension, you can use a ZIP+4 code lookup tool. A ZIP+4 code is a 4-digit code appended to a standard 5-digit ZIP code that helps the USPS sort, route, and deliver mail more efficiently. The last 4 digits of a ZIP+4 code identify a specific group of delivery points within a given ZIP code. You can use the USPS ZIP Code™ Lookup Tool to find the full ZIP+4 code for a specific address or address range. To use the tool, go to the USPS website and navigate to the ZIP Code™ Lookup Tool page, enter your address, and get your +4 Code instantly.