ZIP+4 Code™ Lookup Tool & Last 4 Digits of ZIP Codes Explained

Each of the last 4 digits of ZIP Code numbers explained - They may indicate the specific street, building, or building floor

ZIP+4 Codes are special 4-digit codes appended to 5-digit ZIP Codes that help the USPS to route mail efficiently. When added to mail, the last 4 digits of ZIP Code numbers identify segments of USPS delivery routes.

Each ZIP+4 Code consists of about 10-20 delivery points and could indicate a building, a floor in a high-rise, or one side of a street segment.

ZIP plus 4 codes help prevent misdelivered, lost, delayed, and returned mail. Including those last 4 digit of a ZIP Code can reduce delivery time by as much as 2 days!

Full 9-Digit ZIP Code Lookup

USPS ZIP+4 Code lookups are a cinch with the right tools, and Smarty provides easy-to-use options for single ZIP+4 Code lookups, looking up ZIP+4 Codes in bulk (up to millions at a time), and ZIP+4 Code lookup via API.

Single ZIP+4 Code Lookup Bulk ZIP+ 4 Code Lookup Zip+4 Code Lookup API

In this article; we'll cover:

Video: Find My ZIP+4 Code or Any ZIP+4

Quickly find the last 4 digits of ZIP Code numbers for almost any address in the United States by watching this video.

What ZIP+4 Codes Are

USPS full ZIP+4 Code 9-digit address

ZIP+4 Codes are 4-digit codes appended to the original 5-digit USPS ZIP Codes. Using the full ZIP Code with the extra 4 digits when mailing via the USPS ensures the fastest, most accurate mailing possible.

ZIP+4 Codes are also frequently referred to "Plus-Four Codes", "ZIP Code Extensions", "9 digit ZIP Codes", "Full ZIP Codes", or simply "Extended ZIP Codes". No matter what name you use, ZIP plus 4 codes aid the USPS in sorting and distributing mail effectively.

ZIP plus 4 lookup tools don't just do a full ZIP Code lookup. Before you get the +4 code, your address is taken through the full address standardization and validation process confirm the address is mailable.

These codes indicate a specific delivery route, meaning the actual path the mail truck would travel in a single drop-off. Usually, this comprises ten to twenty homes or locations. The USPS also assigns ZIP+4 Codes to PO Boxes. Typically, each PO Box gets its own +4 Code, which often matches the box number.

The extra 4 digits on ZIP Codes identify segments of fluid postal delivery routes. They're not permanent lines, so a 9 digits ZIP Code can change regularly. Five-digit ZIP Codes also change, but they do so infrequently; it's less likely that you will live in a ZIP Code when it changes. Not so for the last 4 digits of zip code numbers.

The +4 on a ZIP Code can change as frequently as every month. Quantity of postal employees, new construction, remapping delivery areas, etc., are just a few things that cause ZIP+4 Code changes.

Full 9 Digit ZIP Code Benefits (ZIP+4 Lookup)

After the full ZIP Code lookup process is complete 33701-4313

Here are a few benefits of looking up ZIP+4 Codes/9-digit ZIP Codes as a part of your address data management or shipping processes.

  • Faster Shipping - Each ZIP+4 Code represents segments of delivery routes that are usually within a single block of the desired delivery point. That simple 9-digit number makes routing more efficient since the USPS knows which mail person will put the letter in the mailbox. Completing ZIP+4s on your mail can speed up processing and delivery, sometimes by as many as two days.
  • Reduce Lost Mail & Misdeliveries - More efficient routing also means fewer opportunities for mistakes along the way.
  • Less Returned Mail - Obtaining ZIP+4 Codes requires validation; that means the address is a valid delivery point. It also means the address information is standardized to the USPS address format. Mail delivery is more reliable with a valid, standardized address with ZIP4 Code since the address data is clearly understood.
  • Save Money with Bulk Mailings - If you send at least 50 packages or more than 200-500 pieces of mail, you may be able to qualify for commercial mailing discounts. By adding ZIP+4 Codes, Delivery Point Barcodes, and sorting/bundling your mail, you can get discounts up to 5% to nearly 60% off the prices you'd pay at the post office.
  • Cleaner Address Data - Addresses must be validated, standardized, and corrected before you get the ZIP+4 Code. So, you get much more than a pretty 9 digit ZIP Code; you get a clean, standard address. Clean, standard addresses are easy to sort and compare. Comparing a table of standardized, verified addresses allows you to identify duplicates, delete redundancies or merge records easily.
  • Enriched Address Data - When you give Smarty an address and ask for the ZIP+4 Code, we give you the ZIP+4 Code along with the validated, standardized address. We also provide up to 45 data points about the address, including county information, lat/long coordinates, time zone, whether the address is residential or commercial, and more data that can be used for business intelligence and to understand your mail recipients better.

That's right. Your mail can show up faster, cheaper, and more reliably if you label things right, plus you get less returned mail. Bet you're ready to do your first full ZIP Code lookup now.

Those benefits are just the beginning. If you're getting the ZIP+4 code, you're already validating and standardizing the address and address validation unlocks revenue and boosts ROI across all types of organizations. Read our ebook to learn how:

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How ZIP Codes Became 9-Digit-ZIP Codes

ZIP Code Example

Fully understanding the last four digits of ZIP Codes requires knowing about 5-digit ZIP Codes too.

These are the codes you know. They look like this.

The Zone Improvement Plan (ZIP) was something the USPS came up with to make it easier to ship letters and packages across the country. ZIP helps divide the country into different "zones" according to the distribution of mail, which accelerates sorting and delivery.

On July 1, 1963, the Post Office Department launched the Zone Improvement Plan. At the same time, they introduced the world to Mr. ZIP or "Zippy." Zippy is the official ZIP Code mascot pictured on our ZIP Codes 101 page. They also released the ZIP Code jingle:

As the US population has increased and scattered since 1963, it's been necessary to expand the system to make room for everybody and their dog. That's where the "plus 4" part comes in. We're getting ahead of ourselves, so let's start with the basics.

If you're mailing a letter from Boston to Seattle, the mail carrier in Massachusetts doesn't care what the street address of the destination is. It's what you might call "outside his jurisdiction." He just needs to know which mail carrier to send it to so the appropriate mail carrier can get it to the address.

A postal worker can only cover so much ground on a given day. And since the USPS has a standard of delivering in the rain, sleet, or snow, that rules out the possibility of doing the service of delivery in stages (some today, some tomorrow). That means any given post office only serves what it can reach in a day. ZIP Codes reflect that.

Typically, a ZIP Code ties to a post office; by that, we mean every one of the latter has one of the former. You might think of ZIP Codes as a mailing address for a particular post office. Some handle more than one ZIP Code, but a one-on-one game plan is a standard.

It's essential to note that ZIP Codes aren't "boundaries." They're a collection of delivery routes. They don't follow geographic or administrative boundary lines; they can cross city, county, and state lines. They follow where the delivery trucks go.

Some ZIP Codes are a bit different in function. Among them are "military" ZIP Codes, which include everything from military bases (domestic or otherwise) to battleships at sea. Then there are "unique" ZIP Codes. Businesses and organizations sometimes get a dedicated ZIP Code that they don't have to share with anyone due to the volume of mail they send and receive.

These frequently benefit from bulk mailing discounts since the organization usually has a mail department that (1) presorts mail before giving it to the USPS and (2) distributes mail internally, so the USPS doesn't have to. Like standard ZIP Codes, "military" and "unique" ZIP Codes circumscribe their delivery area. For a more in-depth guide, visit our ZIP Codes page.

ZIP+4 Code Database

For many users, the best way to access the USPS ZIP+4 database is through a CASS Certified USPS address validation vendor. Like Smarty. Since the last four digits of ZIP Codes update frequently, even month-old data isn't reliable. Checking addresses regularly against the database will ensure your data remains clean.

The ZIP+4 Code database can be accessed free directly through the USPS site or the USPS address validation API. In our USPS APIs article, you will find a comprehensive list of uses and limitations of the USPS web-based tool and API. If you need a ZIP+4 Code Database, address validation might scratch your itch better than anything provided by the USPS. You can check out our ebook. It shows how to unlock revenue and boost ROI in your organization using address validation. Read it here:

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What Is My ZIP Code with the Extra 4 Digits?

If you need an answer to, "What is my ZIP Code with the extra 4 digits?" Just click one of the buttons at the top of the page, enter your address, and get your +4 code instantly. Just remember, it's called a ZIP+4 Code, or simply a ZIP+4.

The quiz will include three things:

  1. ZIP+4 Codes indicate delivery routes.
  2. Using ZIP+4 Codes gets your mail there faster and more accurately.
  3. We at Smarty can get you those codes.

If you want to try it on a single address, you can now use our Single Address Verification Tool. Our blindingly fast US Address Verification API provides the appropriate ZIP+4 Code for every address we process.

Or you could call us instead if you'd rather talk to an actual person. (We'd offer a fake person, but we don't have one of those on staff.) Either way, we can help you ZIP your address and ZIP it well.

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