What Is an Area Code?
An area code is a three-digit prefix that identifies a specific geographic region within a country's telephone network. In the United States and Canada, area codes are governed by the North American Numbering Plan (NANP), a standardized system that has been in place since 1947. Every phone number in the US follows the format: (NXX) NXX-XXXX, where the first three digits are the area code.
How Area Codes Are Assigned
The North American Numbering Plan Administrator (NANPA) is responsible for assigning and managing area codes. New area codes are introduced when an existing region runs out of available phone numbers — a process called area code exhaustion. There are two main ways a region handles exhaustion:
- Geographic split: The existing area code region is divided into two zones, each getting its own code.
- Overlay: A new area code is added to the same geographic area, so two different codes serve the same region.
Reading a US Phone Number
A standard US phone number like (212) 555-0100 breaks down as follows:
| Part | Digits | Meaning |
|---|---|---|
| Area Code | 212 | New York City (Manhattan) |
| Central Office Code | 555 | Local exchange identifier |
| Subscriber Number | 0100 | Individual line |
Common US Area Codes and Their Regions
Here are some of the most recognized area codes in the United States:
- 212 / 646 / 332 / 917 — New York City (Manhattan & outer boroughs)
- 213 / 310 / 323 / 424 — Los Angeles, California
- 312 / 773 / 872 — Chicago, Illinois
- 713 / 281 / 832 / 346 — Houston, Texas
- 202 — Washington, D.C.
- 305 / 786 — Miami, Florida
- 404 / 678 / 470 — Atlanta, Georgia
Can You Tell a Mobile from a Landline by Area Code?
In the United States, you generally cannot determine whether a number is a mobile or landline based solely on the area code. Unlike many countries (such as the UK or Germany), the US does not reserve specific area codes for mobile phones. This is largely due to number portability, which allows people to keep their number when switching between carriers or even between landline and mobile service.
Toll-Free and Special Area Codes
Not all area codes represent geographic regions. Some are designated for special purposes:
- 800, 833, 844, 855, 866, 877, 888 — Toll-free numbers
- 900 — Premium-rate services (charges apply to the caller)
- 700 — Interexchange carrier services
- 500 — Personal communication services
How to Look Up an Unknown Area Code
If you receive a call from an unfamiliar area code, there are several ways to identify its origin:
- Search the area code on a reverse lookup site or directory.
- Check the NANPA website (nanpa.com) for official area code information.
- Use a caller ID app that cross-references number databases in real time.
Knowing the geographic origin of a call can be the first step in deciding whether to answer or investigate further.