A carrier route is a smaller group of addresses to which the USPS has assigned the same carrier route code. Carrier routes are the last 4 digits of a 9-digit Zip Code, the first 5 numbers are the Zip code, one letter for the carrier route type, and the last 3 numbers are the carrier route number.
Typically a carrier route is actually the route a particular mail carrier delivers and might even be in delivery sequence.
If you’re not sure what carrier route(s) you need, try our Mapping Tool to get a visualization.