ZIP codes within a radius

Worked example: 10 miles around Austin, Texas

The tool opens centered on the Austin capital point with a 10 mile radius. After the ZCTA file loads in your browser, the readout shows how many codes qualify, which one is nearest, and the combined land area of those ZCTAs. The table lists each code with its distance and its own land area from the 2024 Gazetteer.

Widen the radius to 25 miles and watch the list grow. Because each ZCTA is one point, the count rises in steps as the circle passes each internal point, not smoothly as it crosses ZIP boundaries.

ZIP codes and ZCTAs

US Postal Service ZIP codes are delivery routes, not areas with fixed borders. The Census Bureau builds ZIP Code Tabulation Areas (ZCTAs) by assigning census blocks to the ZIP code most common among their addresses. The 2024 Gazetteer lists 33,791 ZCTAs, each with an internal point and a land area. That file is what this tool searches.

Most ZCTA codes match a ZIP code you would write on an envelope. Some ZIP codes, such as those used only for PO boxes or a single large building, have no ZCTA, and a few ZCTAs cover areas the Postal Service splits differently. The Census ZCTA page linked below explains the method.

Edge cases at the circle's edge

A ZCTA counts when its internal point is inside the circle. A large rural ZCTA whose area crosses the circle but whose point is outside will not be listed, even if part of it is only a mile from the center. A ZCTA whose point is just inside will be listed even though most of its land is outside.

For mailing lists and service areas, this is usually what you want: each code is either in or out, with no partial overlaps to resolve. If you need exact coverage, check codes near the edge with the Census boundary files.

Using the list

Copy as list puts the codes on your clipboard separated by commas, ready for a CRM filter or an ad platform's location targeting. The CSV adds the distance in miles and the ZCTA land area in square miles. Rows are sorted by distance, so the first rows are the codes closest to your center.

Territories are included when their ZCTAs appear in the Gazetteer, so circles in Puerto Rico return results too.

How each distance is measured

Distances run from your center to each ZCTA's internal point on a sphere of radius 6,371.0088 km, using the haversine formula, and are shown in miles. A ZCTA qualifies when that distance is no more than the radius you set.

The internal point is a Census-chosen location inside the ZCTA, usually near its middle. It is not a post office and not a population center. For a long, narrow ZCTA the point can sit far from where most of its addresses are, which is one more reason to check codes near the circle's edge.

The land area column is the whole ZCTA's land in square miles from the Gazetteer, not the part inside your circle. Adding it up tells you the footprint of the codes you selected, which is usually larger than the circle itself.