🇺🇸 United States Phone Number Format
United States phone numbers follow the North American Numbering Plan (NANP): a 3-digit area code, a 3-digit central office code, and a 4-digit line number — 10 digits total behind country code +1. In E.164 they are written as +1 followed by all 10 digits, with no spaces or punctuation.
One US Number, Four Standard Formats
Here is how one United States number is written in each of the four standards:
| Format | Example | Use for |
|---|---|---|
| E.164 | +14155550132 | Databases, SMS APIs (Twilio, WhatsApp), CRMs |
| International | +1 415 555 0132 | Display to a global audience, business cards |
| National | (415) 555-0132 | Domestic display inside United States |
| RFC3966 | tel:+1-415-555-0132 | Clickable tel: links on websites |
How the North American Numbering Plan Works
The NANP is the world’s oldest closed numbering plan, designed by AT&T in 1947 to let operators connect long-distance calls without a human switchboard. Today it covers 25 countries and territories under the single country code +1 — which is why a number alone can’t tell you whether you’re calling San Francisco or Toronto until you read the area code.
NANP rules are stricter than most plans: both the area code and the exchange code must start with a digit from 2–9, and codes ending in 11 (211, 911…) are reserved for services. That’s why a formatter can instantly reject “(123) 456-7890” — 123 is structurally impossible — while a naïve length check would accept it.
Number portability has loosened geography over time: a 415 mobile may live in New York these days. Treat US area codes as a hint of origin, not a guarantee of location.
NANP Area Codes and the 555 Range
Type Prefixes Digits Example Mobile & landline Area codes 201–989 (no leading 0 or 1) 10 (415) 555-0132 Toll-free 800, 833, 844, 855, 866, 877, 888 10 (800) 555-0199 Premium rate 900 10 (900) 555-0144
Dialing US Numbers at Home and from Abroad
Calling from Dial Within the US 415 555 0132 or 1 415 555 0132 — The leading 1 is the domestic trunk code. From the UK 00 1 415 555 0132 From any mobile +1 415 555 0132 — The + form works worldwide.
- Enter the international prefix of the country you are calling from (or just +).
- Add the US country code 1.
- Dial the 3-digit area code, e.g. 415.
- Dial the remaining 7-digit subscriber number.
US Numbering Quirks Worth Knowing
- The US shares country code +1 with Canada and 23 other NANP territories — the area code identifies the region.
- US mobile and landline numbers are indistinguishable by format; both use the same 10-digit pattern.
- Numbers in the 555-01XX range are officially reserved for fictional use, which is why examples use them.
- SMS APIs such as Twilio require the E.164 form +1XXXXXXXXXX with no formatting characters.
Major US Area Codes
Area code Region 212 / 646New York City (Manhattan) 415 / 628San Francisco 312 / 872Chicago 213 / 323Los Angeles 305 / 786Miami 202Washington, D.C. 512 / 737Austin 206Seattle
Format a US Number Instantly
Paste any US number — with or without the +1, parentheses, or dashes — and get clean E.164, international and local formats in one step.
Enter phone number with country code or select country below.
Up to 100 numbers. Include country code or select a default country below.
| Original | E.164 | International | National | Valid |
|---|
US Phone Format: Common Questions
What is the correct format for a US phone number?
Domestically: (415) 555-0132 or 415-555-0132. Internationally and for databases or SMS APIs, use E.164: +14155550132 — country code 1 plus the 10-digit number with no separators.
How do I write a US number with country code?
Prefix the 10-digit number with +1: +1 415 555 0132. In strict E.164 (for APIs and CRMs) remove all spaces: +14155550132.
Do I dial 1 before US numbers?
Within the US, the leading 1 is required for long-distance calls and optional on most mobiles. From abroad you always include it as the country code: +1.
Can a US phone number start with 0 or 1?
No. NANP area codes and exchange codes must start with digits 2–9. A leading 0 or 1 in either position makes the number invalid.
Are US mobile numbers different from landlines?
No — unlike most countries, US mobile numbers use the same geographic area codes and 10-digit format as landlines, so you cannot tell them apart from the number alone.