How the tool finds your ZIP code
Your browser asks your device for its position, which on a phone usually comes from GPS and Wi-Fi and is accurate to a few meters outdoors. The tool then makes two lookups at once. OpenStreetMap’s Nominatim service finds the nearest street address and the ZIP code recorded with it, which is the ZIP you would write on an envelope. The U.S. Census Bureau’s geocoder reports which official areas the point falls in: the Census ZIP area, county, city or town, congressional and state legislative districts, and school district.
Only the coordinates are sent to those services, and nothing is stored by this site. If the Census service is slow or down, the county and state come from the FCC’s Area API instead. See the Privacy Policy for details.
What is my current ZIP code?
Your current ZIP code is the one for where you are standing now, which is not always the one on your mail when you are traveling or at work. Press the button in the tool above and it finds the ZIP code of your location from your device’s position, with the county, city and districts for the same spot. To check a ZIP code you already have, type it in instead and the tool shows the county and state for its center.
How ZIP codes work
The Postal Service introduced ZIP codes, for Zone Improvement Plan, in 1963, and today there are about 42,000 of them. The five digits narrow down step by step:
| Digits | Example (10118) | What they identify |
|---|---|---|
| First digit | 1 | A group of states, from 0 in the Northeast to 9 on the West Coast, Alaska, and Hawaii. 1 covers New York, Pennsylvania, and Delaware. |
| First three | 101 | The sectional center facility, the mail processing plant that serves the area. |
| All five | 10118 | The delivery area: a post office's routes, a town, or, as here, a single building (the Empire State Building). |
| ZIP+4 | 10118-#### | Four more digits for a block, one side of a street, a floor, or a large mail recipient. |
The key point is that a ZIP code is a set of mail delivery routes, not an area with an official boundary. That is why it does not tell you your county or district on its own.
ZIP code or Census ZIP area?
Because ZIP codes are routes, the Census Bureau draws its own approximation of them as areas, called ZIP Code Tabulation Areas (ZCTAs), built from census blocks. There were 33,791 ZCTAs in the 2020 Census, against roughly 42,000 ZIP codes. The missing ones are mostly ZIP codes for P.O. boxes only and for single buildings or organizations, which have no area of their own.
The tool shows both. At the White House, the mailing ZIP is 20500, but the Census area is 20006. At the Empire State Building, the mailing ZIP is 10118 and the Census area 10001. On an ordinary street the two are usually the same. When they differ, use the mailing ZIP for post and forms, and the Census area only for statistics.
Why a ZIP code alone cannot tell you your county or district
- ZIP codes cross county lines. Many rural ZIP codes, and plenty of suburban ones, cover parts of two or more counties. Property tax, voting, jury service, and court cases all follow the county, so use the exact location.
- Districts are drawn from census blocks. Congressional, state senate, and state house districts follow census blocks, which split ZIP codes freely. Two houses with the same ZIP can be in different districts.
- Cities are not ZIP codes either. The place name in a mailing address is the post office’s, which can differ from the town you actually live in. The tool shows the incorporated city or town from the Census Bureau, or the township or census subdivision where there is none.
That is why the tool looks up your location rather than your ZIP code for these. When you type a ZIP code, the county and districts shown are for its center, and the result says so.
When the result might not be yours
- Rough location fix. Indoors, or on a laptop without GPS, your position can be 50 m or more out, enough to land on the next street or across a boundary. The tool warns you when your device reports low accuracy.
- You live near a boundary. ZIP, county, and district lines often run down the middle of a road. Click your own building on the map to be sure.
- The map has no address for your building. OpenStreetMap is edited by volunteers, and some new or rural addresses are missing. The tool then falls back to the Census ZIP area and says so.
For anything official, such as voter registration, confirm with the source: the USPS ZIP code lookup for mail, and your state or county election office for districts.