ZIP+4 Codes™ Lookup by Address | 9-digit ZIP Codes

ZIP+4 Code Lookup - Full 9-digit ZIP Codes Explanation Displayed

ZIP+4 Codes (ZIP Plus 4 Codes) are the final 4 digit codes of full 9-digit ZIP Codes. The 9-digit ZIP Code consists of two sections. The first five digits indicate the destination post office or delivery area. The last 4 digits represent specific delivery routes within delivery areas.

ZIP plus 4 codes assist the USPS in effectively sorting and distributing mail.

9-digit Full ZIP Code Lookup by Address

We make it easy to perform a USPS full ZIP+4 Code lookup by address. Choose your option below to find your ZIP+4 Code.

Enter an address to lookup the specific ZIP+4 Code. Lookup several ZIP+4 Codes at once with the Bulk Tool. Lookup ZIP+4 Codes programmatically using our API.

In this article we'll cover:

How to Find My ZIP+4 Code by Address

You can easily find out your own ZIP+4 last 4-digits by watching this video which shows you how to do it in under a minute.

How Full ZIP Codes Are Used

Knowing what the last four digits of ZIP Codes are all about requires knowing what ZIP Codes themselves are all about. The Zone Improvement Plan was something that the USPS came up with to make it easier to ship letters and packages across the country. It helped divide the country into different "zones" according to how mail was distributed, which accelerated sorting and delivery.

At the same time that the Post Office Department launched the Zone Improvement Plan on July 1, 1963 they also introduced the world to Mr. ZIP "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 on 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, though, so let's start with the basics.

USPS Five-Digit ZIP Codes

ZIP Code Example

These are the codes you're familiar with.

They look like this…

…and most commonly indicate a destination post office. Here's why:

If you're mailing a letter from Boston to Seattle, the mail carrier in Massachusetts doesn't really 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 other carrier can get it to that address.

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

Typically, a ZIP Code is tied 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 do handle more than one ZIP Code, but a one-on-one game plan is the norm.

It's very important 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, or even state lines. They follow where the delivery trucks go.

Some ZIP Codes are special cases. 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 their own ZIP Codes, due to the volume of mail they send and receive. These are frequently benefiting 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 own delivery area. For a more in depth guide, visit our ZIP Codes page.

ZIP Code + 4 Meaning

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 full ZIP Codes when mailing with the USPS ensure the fastest, most accurate mailing possible. ZIP+4 Finder tools don't just lookup the full ZIP Code. The +4 is only provided once the address has been standardized, validated and proven real. 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. ZIP+4 Codes are also assigned to PO Boxes. Typically, each PO Box gets its own +4 Code, which often matches the box number.

Because ZIP codes plus 4 extra digits are based on delivery routes instead of more permanent boundaries, the last 4 digits of a complete ZIP Code can change often. Five-digit ZIP Codes also change,but they do so infrequently; it's a lot less likely that you will be living in a ZIP Code when it changes. Not so for the full 9-digit ZIP Code. The +4 on a ZIP Code can be changed as frequently as once a month, based on things like how many postal employees are working, or who is working what route, etc.

Full ZIP+4 Code Lookup Benefits

The full 9-digit zip code after lookup? 33701-4313

There are a number of reasons that looking up and using full ZIP+4 Codes are good omens for your shipping. For one, ZIP+4 Codes require validation; that means you know for sure an address is real if it has a ZIP+4 attached to it. For another thing, they can help get you those bulk mailing discounts.

Another important benefit to using the last four digits of ZIP Codes is delivery speed. Using complete ZIP+4 on your mail can speed up processing and delivery, sometimes by as much as two days. That's right, your mail can show up faster if you label things right. Bet you're scrambling to lookup those full ZIP Codes now, huh? Get those extra 4 digits.

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 against the database regularly will ensure your data remains clean.

The ZIP+4 Code database can also be accessed free directly through the USPS site or through the USPS address validation API. A comprehensive list of uses and limitations of the USPS web-based finder and API can be found in our USPS APIs article.

Conclusion | What is My +4 ZIP Code?

If you want to ask, "What is my +4 ZIP Code?" All you need to do is use one of the three buttons at the top of the page, enter your address and you will have your +4 code instantly. That was easy!

Three things will be on the quiz:

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

If you want to try it on a single address, you can use our single address verification tool now. Our blindingly fast USPS address verification API provides the appropriate ZIP+4 Code for every address we process. Go ahead and perform some postal address verification. Or you could call us instead if you'd rather talk to a real 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 good.

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