US Phone Number Format: Rules, Examples and How to Validate One

A US phone number has 10 digits: a 3-digit area code and a 7-digit local number, preceded by country code +1. Store it in E.164 as +14155552671; show it to people as (415) 555-2671. To be valid, the area code and the next three digits (the exchange) must both start with 2–9, and the area code must actually be assigned.

The structure

+1  (415)  555 - 2671
 │    │     │      └─ line number (4 digits)
 │    │     └─ exchange code (3 digits, starts 2–9)
 │    └─ area code (3 digits, starts 2–9)
 └─ country code, shared across the North American Numbering Plan

The US shares +1 with Canada and around 20 Caribbean and Atlantic countries and territories, all under the North American Numbering Plan. So +1 alone doesn't mean the US: +1 876 is Jamaica, +1 604 is Vancouver.

The rules that make a US number valid

1. Exactly 10 digits after the country code.
2. Area code starts 2–9. (012) 555-1234 is invalid.
3. Exchange code starts 2–9. (212) 123-4567 and (212) 055-1234 are invalid.
4. The area code has to be assigned. (555) 123-4567 looks fine but 555 isn't an area code, so it's invalid.
5. N11 codes aren't numbers. 211, 311, 411, 911 and the rest are service codes, not area codes or exchanges.

We ran each of those examples through Google's libphonenumber (version 9.0.41) to confirm the result. Everything a regex can't know, like whether an area code is assigned, comes from numbering-plan data like this.

Which format to use where

Where	Format	Example
Database, CRM, APIs, SMS	E.164	+14155552671
Website, email signature (US audience)	National	(415) 555-2671
International audience	International	+1 415-555-2671
Clickable link on a web page	tel: URI	tel:+14155552671

Store one format, display another. If your CRM holds (415) 555-2671 in one record and 415.555.2671 in another, it won't match them as duplicates. E.164 makes them identical. More in E.164 format explained.

Toll-free and premium numbers

Prefix	Type
800, 833, 844, 855, 866, 877, 888	Toll-free
900	Premium rate

Toll-free numbers are free for the caller and are often company main lines. A lead list full of 800 numbers is a list of switchboards, not people.

Numbers that pass validation but aren't real

"Valid" means the number is in an allocated range, not that someone uses it. Three cases to know:

• 555 numbers. (212) 555-0100 validates as a New York number, but 555-0100 to 555-0199 is reserved for fiction and examples. We cover the whole 555 story in 555 phone numbers.
• Disconnected numbers. They stay in valid ranges until reassigned.
• Reassigned numbers. A valid, working number may belong to someone new. The FCC's Reassigned Numbers Database exists for exactly this.

Mobile or landline?

You can't tell from the digits. US mobile and landline numbers come from the same area codes, and since 2003–2004 people have been able to port a number from a landline to a mobile carrier and back. A free validator returns "mobile or landline" for almost every US number. Splitting them takes a carrier lookup. See mobile vs landline lookup.

Validating a list of US numbers

1. Make sure the phone column is text, so the + and digits survive spreadsheet software.
2. Convert to E.164 with US as the default country. 415-555-2671, (415) 555 2671 and 1-415-555-2671 all become +14155552671.
3. Remove anything invalid, then deduplicate on the E.164 value.

In SimpleVerifier, upload the CSV on the verifier and every row gets phone_status, phone_e164, phone_country and phone_type. Numbers without a country code are read as US numbers by default. It's included in the $29.99 plan. Full walkthrough: how to clean phone numbers in a CSV.

Related: UK phone number format · phone validation for cold calling