Example result
ZIP code 10003, looked up through the public postal-code service.
- ZIP code
- 10003
- Place
- New York City
- State
- New York (NY)
- Approximate centre
- 40.7313, -73.9892
- 3-digit prefix
- 100
- National area
- 1: Second area from the east, counting 0 as the first.
Captured 2026-10-19.
How it works
- Type a ZIP code. Five digits work, and so does ZIP+4 such as 12345-6789 or the form ZIP 12345. Leading zeros count, so type 02108 and not 2108.
- The page checks the shape first, then looks up the first five digits in a public postal-code service that needs no key. A code the service does not hold comes back as not found. A service that does not answer comes back as an error you can retry.
- The result lists every place the code covers, the state, the approximate centre of each place and what the first digit and the 3-digit prefix mean.
What a ZIP code is
A ZIP code is a number the United States Postal Service uses to sort and deliver mail. The Census Bureau describes it as a code the USPS assigns to regional post offices, which in turn assign it to delivery routes. A route is made of street networks, or of single addresses with a lot of mail such as a tall building or a business.
So a ZIP code names a set of delivery routes. It is not a map boundary, and it was never drawn as one. That is why a ZIP code lookup returns a place name and a point, not an outline.
Why a ZIP code can cross city or state lines
Delivery routes follow the way mail is carried, not the lines on a political map. A route can run along a street that is the border between two cities, or serve homes on both sides of a county line, and the code follows the route. Some codes also list more than one place name because several communities share one post office.
This page therefore lists every place the service holds for the code, each with its own centre. When a code shows several places, none of them is wrong: the mail for all of them is sorted under the same five digits.
ZIP code versus area code
A ZIP code and an area code are different systems that happen to have a similar shape. A ZIP code is five digits and sorts mail. An area code is three digits and routes phone calls within the North American numbering plan. One ZIP code can sit inside the area of several area codes, and one area code can cover hundreds of ZIP codes. Neither one is derived from the other.
To look up a phone prefix instead, use the area code pages on this site. Knowing a ZIP code tells you nothing certain about a phone number, and the reverse is also true.
ZIP code versus ZCTA
Census data is not published by ZIP code. The Census Bureau builds ZIP Code Tabulation Areas, or ZCTAs, which are areas made from census blocks that approximate the ZIP codes. The Bureau gives the reason: ZIP codes are stored as points tied to delivery addresses, which are unsuitable to publish and to map, so it aggregates them into areas.
A ZCTA and a ZIP code often share the same five digits but are not the same thing. If you join census figures such as population or income to a ZIP code, you are joining to the ZCTA, and the two can differ at the edges.
What this page shows
The page shows the places a ZIP code covers, the state and an approximate centre point.
A ZIP code the service does not hold shows as not found. That covers codes that were never assigned and codes that are not in the service, and it is different from an error, which means the service did not answer.
How to read a ZIP code: the first digit on the national scale, and what each part of the digits stands for
| Part of the code | What it stands for | Detail |
|---|---|---|
| First digit 0 | National area | The eastern end of the scale. The lowest assigned ZIP code, 00501, is in Holtsville, New York. |
| First digit 1 | National area | Second area from the east, counting 0 as the first. |
| First digit 2 | National area | Third area from the east. |
| First digit 3 | National area | Fourth area from the east. |
| First digit 4 | National area | Fifth area from the east, the middle of the scale. |
| First digit 5 | National area | Sixth area from the east, the middle of the scale. |
| First digit 6 | National area | Seventh area from the east. |
| First digit 7 | National area | Eighth area from the east. |
| First digit 8 | National area | Ninth area from the east. |
| First digit 9 | National area | The western end of the scale. The highest assigned ZIP code, 99950, is in Ketchikan, Alaska. |
| Digit 1 | A general area of the country | USPS describes the first number as a general geographic area, 0 in the east moving to 9 in the west. |
| Digits 1 to 3 | A regional area | The first digit with the next two numbers makes the 3-digit prefix. USPS groups prefixes under sectional center facilities that sort mail for a region. |
| Digits 4 and 5 | A specific Post Office | The final two digits of the five-digit code identify specific Post Offices. |
| The +4 part | A street or a block | Added in 1983. The extra four numbers let mail be sorted to a specific street. |
Sources
- Zippopotam.us, the postal-code API this page reads (usage, license and data origin) read 2026-10-19
- GeoNames, the data origin of the postal-code service read 2026-10-19
- USPS Postal Facts: Introduction of the ZIP Code (meaning of the digits, ZIP+4, first and last assigned codes) read 2026-10-19
- USPS FAST labeling list L005: 3-digit ZIP Code prefix groups and the sectional center facilities that serve them read 2026-10-19
- US Census Bureau: ZIP Code Tabulation Areas (ZCTAs) and how they differ from ZIP codes read 2026-10-19
This tool is run by LookValid. It is not connected to any agency, company or service named on this page.
Frequently asked questions
Does a ZIP code match a city boundary?
Not exactly. A ZIP code names a set of delivery routes, so it can cover parts of more than one city or county. The page lists each place the service holds for the code so you can see when a code is shared.
Why is a leading zero kept?
A ZIP code is text, not a number. Codes in the northeast start with 0, such as 02108 for Boston, and 2108 is not a valid code. Type all five digits.
What happens with a ZIP+4?
Only the first five digits are looked up. The extra four digits narrow a delivery route to a street or a block, and the postal-code service this page reads does not hold them.
Is the centre point exact?
No. It is the approximate centre of each place the code covers, rounded to four decimals. Do not use it to find an address or to measure a delivery route.
Why does the page say a code was not found?
The service has no entry for it. The code may be unassigned, such as 00000, or retired, or mistyped. A service that fails to answer is reported as an error with a retry button, never as not found.
Is a ZIP code the same as an area code?
No. A ZIP code has five digits and sorts mail. An area code has three digits and routes phone calls. They are separate systems and neither is derived from the other.
Where does the place data come from?
The data comes from GeoNames under the CC BY 4.0 license, served by the public Zippopotam.us postal-code service, which publishes its API under the Open Database License. The Postal Facts and Census pages in the sources list explain the digits and the ZCTA.