Your Source of Information on Postal Carrier Routes, Saturation Mailing, and Carrier Route Maps

This site was created as a service for all businesses and organizations that have questions about the creation and importance of carrier routes and how they impact direct mailing.

Feel free to have your webmaster create a link from your site directly to this site and refer your customers here to answer their frequently asked questions. If you've never managed a direct mail campaign before, you should check out the great USPS Discount Mailing Services webpage.

Please Note: This site offers information related to carrier routes in general. It is not designed to answer specific questions about delivery times or assignments of carrier routes. For assistance with mail delivery issues, please contact your local branch of the US Postal Service.

Carrier Route Definitions

What is a carrier route?

A postal carrier route is the group of addresses to which the USPS assigns the same code to aid in mail delivery. These codes are 9 digits – 5 numbers for the ZIP Code, one letter for the carrier route type (explained below), and 3 numbers for the carrier route code. For example "05055R003" or "12508C007." Typically, each carrier route is related to where a particular mail carrier delivers.

How many carrier routes and ZIP Codes exist?

There are approximately 600,000 unique carrier routes in the US. Of these, approximately half are assigned to post-office boxes, leaving approximately 300,000 that represent “boundaries” or delivery areas. These numbers fluctuate from month to month. Since there are approximately 40,000 valid ZIP Codes in the US that translates to an average of 15 carrier routes per ZIP Code. Obviously any particular ZIP Code could have many more or many fewer than this average.

Do carrier routes change?

Yes. The USPS makes minor changes to the delivery routes continuously, usually due to either population or staff changes. For example, as new homes are built, those new addresses must be added to a carrier’s delivery route. Budget changes at local post offices can also impact delivery definitions because of staff or technology modifications. Most of these changes are minor – adding or deleting a few streets or moving a few addresses from one carrier route to another. However, sometimes an entire delivery system for a county can be disrupted as entire ZIP Codes are added or subdivided.

While the change can be initiated by local post offices, the USPS headquarters in Memphis, TN is the only entity to aggregate individual carrier route change information nationally. They release a monthly database of all carrier route definitions. There are many independent companies that license various subsets of this database to help other businesses ensure that large mailings are addressed efficiently for delivery.

How often do carrier routes change?

Somewhere in the US, a carrier route changes every day. The USPS releases a monthly database of the latest definitions, but it does not “track” the changes per se. Some changes are very subtle – one new address added because a new home was built at the end of a street – and so tracking the type of change is an expensive effort few commercial organizations have undertaken.

How many CR changes are there nationally on a monthly basis?

Nationwide, each month you can expect at least 100,000 changes (adds, deletes, or modifications) to the carrier route definitions. That represents more than 15% each month!

Do carrier routes follow ZIP Codes?

Each carrier route is explicitly defined as part of a single ZIP Code. The full 9 digits of the carrier route code (e.g. 12508C007) is a unique code that represents each carrier route and so, by definition, it cannot cross multiple ZIP Codes.

What is the difference between a carrier route code and a ZIP+4 code?

Although a ZIP+4 code also has 9 digits, it is not the same as a carrier route code. There are far more ZIP+4 codes in the US – approximately 40,000,000, usually assigned to one side of a street block. Each carrier route contains tens or hundreds of ZIP+4 codes. Additional info on ZIP+4 maps and lists can be found on the web. What does the first letter in front of a carrier route label mean? Is there a difference between R001 and C001 - does the R or C designation affect my ability to direct mail to these areas?

Carrier routes can be sub-characterized as city, rural, PO Box, or highway contract routes - each based on what kind of delivery mechanism is used. The letter at the start of the carrier route number indicates the sub-characterization. The designation "R" denotes a rural delivery carrier route where mail is delivered via automobile. A "C" designation means that it is a city delivery route, where mail is delivered on foot by a postal service employee. The designation "B" indicates that is "PO box delivery". These carrier routes cannot be mapped by mapping firms because multiple labels overlap significantly. Regardless of the sub-characterization, all postal discounts allowed for mailing by carrier route will apply. While these letter-based designations can give you some idea of the density of occupants to expect in any given carrier route, they do not limit your ability to send direct mail.

Do all carrier routes include businesses, apartments and single family homes?

The USPS does not usually define carrier routes by the type of occupant receiving mail: any given carrier route could include any or all of the above types of recipients. However, it is possible to get summary counts for any carrier route from your list provider or mapping service bureau showing the number of deliverable addresses for businesses, MFDUs (multi-family dwelling units), and SFDUs (single family dwelling units). You can use this data to target your mailings to carrier routes heavy in the type of recipient of interest to you.

Does Canada have the equivalent of a carrier route?

Canada’s postal system is designed a little differently than that in the US. Canada uses a 6-digit code, called the “FSALDU”, where the FSA is similar to a US ZIP Code and the LDU is more akin to a US ZIP+4.

Mailing by Carrier Route

What is a “saturation” mailing?

A saturation mailing is simply any mailing campaign that mails to at least 90% of the residential addresses within a postal carrier route. Many mailers erroneously think that a saturation mailing must be conducted by ZIP Code but the actual definitions from the USPS for the maximum saturation discount uses the carrier route as the defining region. Also check out the great USPS Discount Mailing Services webpage at .

What is the postal discount for doing a saturation mailing by carrier route?

When you mail by saturating a carrier route, you can expect to save between 50-60% on your mailing postage costs. Similar savings can be obtained by doing a “high density” mailing where you mail to at least 125 addresses in a carrier route. For the most current rates, you should work with your lettershop or list provider, or call you local post office. For current postal rates, click here.

Why does the USPS offer discounts for “saturation mailings”?

When you prepare your mailing according to USPS guidelines, including meeting the saturation criteria, it makes the post office’s job easier. It reduces the time-consuming coding and sorting that is part of the USPS's mail delivery process.

Who normally mails by carrier route?

Any business attempting to reach the majority of residents in a localized area should mail by carrier route.

What is a resident occupant list?

A resident occupant list is a list of addresses of all residents in a particular area, prepared by a commercial list provider. It comes pre-sorted and saturated by carrier route and guarantees the maximum postal discounts.

Can I get a carrier route code appended to my address file? What is CASS?

All major direct mail campaigns should be running the address files through an address standardization process known as "CASS," following strict USPS guidelines. Even non-saturation mailings should be CASS certified prior to mailing to ensure the maximum delivery. CASS checks the addresses against a USPS file of deliverable addresses, corrects any typos in your address file, appends the ZIP+4 and carrier route codes (along with some other codes not relevant to this discussion). Your list provider should always run the list against a CASS process before giving it to you, but your lettershop or other service bureau can CASS your existing customer database for you. You can also use carrier routes to target new customers.

If we have traditionally used ZIP+4s to organize our data – what are the advantages of switching to CRs and how would we go about it?

Because your file should always be CASS certified (see previous question), you will always have both a ZIP+4 code and a carrier route code on your address file. However, the maximum postal discount only applies when mailing to at least 90% of the residential addresses within a carrier route. There are comparatively minimal discounts for mailing by ZIP+4. Hence “mailing by carrier route” is usually most advisable.

For service bureaus that analyze your files, it is also a lot easier to work with the smaller carrier route database (~600,000 records) than the large ZIP+4 database (~40,000,000) so data processing costs are generally much lower for files sorted by carrier route.

Are demographics available by carrier route?

Many demographic data providers are able to generate statistics on income, age, and other demographics based on carrier route.

Carrier Route Boundaries Map Data

Through an extremely complex process, the address data released by the USPS is matched to street map databases. The resulting street segments are then grouped together to form a “boundary”. Sometimes these boundaries are discontinuous – a carrier route may be represented by more than one polygon when a mail carrier delivers to non-adjacent neighborhoods in a ZIP Code. The process of generating these carrier route map polygons is surprisingly NOT performed by the USPS. Private companies like Maponics generate these boundaries. Call 1.800.762.5158 to learn more, or email

Carrier Route Mapping

What is a carrier route map?

A carrier route map simply shows the geographic boundaries that delineate carrier routes. You can download a sample carrier route map (opens in PDF format) here.

What is a carrier route centroid?

A carrier route centroid is simply the center point of the carrier route boundary polygon.

Do carrier routes follow ZIP Codes? Can a carrier route cross more than one ZIP code?

If the company creating the carrier route boundaries is using accurate data and a reliable process, carrier routes should never cross a ZIP Code. The best mapping providers update their carrier route data monthly, which is as often as the USPS updates its official records, and have 100% synchronization with their ZIP Code data.

What’s the difference between a carrier route map and a carrier route report?

Carrier route reports list the carrier routes for each ZIP Code in a spreadsheet (click here for a sample). These reports can also list delivery counts or other demographics.

Why do companies use carrier route maps for direct mailing?

By mailing to entire carrier routes rather than entire ZIP Codes, you can still qualify for the maximum postal saturation discounts while you eliminate areas where you will not likely get a response. By using a map, you can actually see where those carrier routes are located relative to your market.

Why would a company use carrier route maps instead of ZIP+4 maps?

Because there are almost 100 times as many ZIP+4s than carrier routes, it is nearly impossible to map and label all the ZIP+4s in an area larger than a few hundred feet. Plus, mailing by ZIP+4 offers minimal postage discounts compared to carrier route saturations.

How does a resident occupant list relate to a carrier route map?

A resident occupant list is a prepared list of addresses of all residents in a particular area. It comes pre-sorted and saturated by carrier route and guarantees the maximum postal discounts. With a corresponding map, you can locate those carrier routes on a map and eliminate carrier routes you don’t want to mail to. The best use of the map comes before purchasing an address file. By seeing those carrier routes mapped out, you can only order the addresses you really need. This saves money on lists, printing, and postage. You can find resident occupant lists as well as consumer and business address lists at the Maponics Online Store.

Why does my resident occupant list show a carrier route that isn’t on the carrier route map?

List compilers and map data compilers have different operating schedules and it is nearly impossible to ensure 100% synchronization between the two, especially since the data sources (USPS and commercial street map data) change every day. Occasionally, carrier route maps and resident lists have minor discrepancies.

Are demographics available by carrier route?

Many demographic data providers are able to generate statistics on income, age, and other demographics based on carrier route and these can be easily added to maps by professional mapping service bureaus. However, getting accurate carrier route demographics is not easy. See our page on carrier route demographics for some guidelines to watch for.

Who provides carrier route maps? Can’t I get carrier route maps through the USPS?

The USPS does not provide maps, instead they refer their business customers looking for carrier route or ZIP Code maps to the Maponics Online Store. You can look up the carrier route code for individual addresses on though. Click here for some links to website lookups.

How can I tell if a carrier route map is accurate and useful?

There are many things to check for when comparing mapping quality. Maponics has developed a good set of considerations that you can view by clicking here.

What does it mean if there is a portion of my ZIP Code without a carrier route code?

There are parts of the country that do not have USPS mail delivery. Database compilers, particularly mapping companies, generate ZIP Code maps for the whole US such that there are no gaps between ZIP Codes. However, it would be misleading to do so for carrier route areas. If a portion of a map shows no carrier route boundaries, it likely means that there are insufficient deliveries in the area, which is instead probably served through a PO box.

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More Information:

Carrier Route Maps
ZIP Code Maps
Address Lists and Demographics
Carrier Route Data
ZIP Code Data
ZIP+4 Data

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