Phone Number Format: US & International Number Structure Guide (2026)
Complete guide to phone number formats. Learn the US NANP structure (10 digits), E.164 international standard, area code rules, special numbers (911, 555, toll-free), and how to format numbers for dialing and databases.
A US phone number has 10 digits: a 3-digit area code + a 7-digit local number. With the country code +1, it's 11 digits total. The international standard for formatting phone numbers is E.164, which uses a maximum of 15 digits and the format +[country code][number].
This guide explains how phone numbers are structured in the US and worldwide: the NANP system (created in 1947), area code rules, special numbers (911, 555, toll-free), international formats for 10+ countries, and how to properly format numbers for dialing, databases, and HTML links. Whether you're making a call or building an app, this is the definitive reference.
Anatomy of a US Phone Number
+1 (212) 555-1234
Country Code
+1
US & Canada
Area Code (NPA)
212
3 digits, 1st: 2-9
Exchange (NXX)
555
3 digits, 1st: 2-9
Line Number
1234
4 digits, 0-9
The NANP (North American Numbering Plan) format is NPA-NXX-XXXX, where N = digits 2-9 and X = digits 0-9. Area codes and exchange prefixes can never start with 0 or 1.
US Phone Number Rules (NANP)
| Component | Digits | Rules | Example |
|---|---|---|---|
| Country Code | 1 | Always +1 for US/Canada | +1 |
| Area Code (NPA) | 3 | First digit 2-9, digits 2-3: 0-9 | 212 |
| Exchange (NXX) | 3 | First digit 2-9, digits 2-3: 0-9 | 555 |
| Line Number | 4 | All digits 0-9 | 1234 |
Total: 10 digits (without country code) or 11 digits (with +1). The digit 0 is reserved for the operator, and 1 is the long-distance prefix — that's why neither can start an area code or exchange.
A Brief History of US Phone Numbers
AT&T and the Bell System created the North American Numbering Plan in 1947, establishing 86 original area codes across the US and Canada. The system was designed around rotary dial phones — each digit required a specific number of pulses, so high-population areas got the lowest numbers (fewest pulses).
| City | Area Code | Dial Pulses | Why |
|---|---|---|---|
| New York City | 212 | 5 pulses (2+1+2) | Largest city → fastest to dial |
| Los Angeles | 213 | 6 pulses (2+1+3) | Second-largest city |
| Chicago | 312 | 6 pulses (3+1+2) | Third-largest city |
| Detroit | 313 | 7 pulses | Fourth-largest at the time |
| Dallas | 214 | 7 pulses | Major Texas city |
Originally, area codes with 0 as the middle digit went to states with one area code (e.g., 203 for all of Connecticut), and codes with 1 as the middle digit went to states needing multiple codes (e.g., 212/518 for New York). This rule was eliminated in 1995.
International Phone Number Formats
The E.164 standard (ITU-T) defines the universal format: +[country code][subscriber number], with a maximum of 15 digits. Here's how phone numbers are formatted in the most-called countries:
| Country | Code | Digits | Example (E.164) |
|---|---|---|---|
| United States | +1 | 10 | +12125551234 |
| United Kingdom | +44 | 10-11 | +442079460958 |
| India | +91 | 10 | +919876543210 |
| China | +86 | 11 (mobile) | +8613912345678 |
| Japan | +81 | 10-11 | +81312345678 |
| Germany | +49 | Variable | +49301234567 |
| Australia | +61 | 9 | +61412345678 |
| Brazil | +55 | 11 (mobile) | +5511987654321 |
| Mexico | +52 | 10 | +525512345678 |
| France | +33 | 9 | +33123456789 |
Key rule: When dialing internationally, always drop the trunk prefix (leading 0). A UK number 020 7946 0958 becomes +44 20 7946 0958.
Special US Phone Numbers
N11 Service Codes
| Code | Service |
|---|---|
| 911 | Emergency services (police, fire, ambulance) |
| 211 | Community services and information |
| 311 | Non-emergency city/county services |
| 411 | Directory assistance (reserved) |
| 511 | Traffic and road conditions |
| 611 | Phone company customer service |
| 711 | Telephone Relay Service (hearing impaired) |
| 811 | Call Before You Dig (underground utilities) |
| 988 | Suicide & Crisis Lifeline (since July 2022) |
Toll-Free Numbers
Toll-free numbers are free for callers — the receiving business pays. They use special area codes:
555 Numbers (Fictional)
Numbers 555-0100 through 555-0199 are officially reserved for movies, TV, and books. This convention started in the early 1960s after viewers kept calling numbers they saw on screen, harassing real subscribers. Numbers outside this range (555-0200 onwards) can be commercially assigned.
How to Format a Number for International Dialing
From US to UK
UK domestic: 020 7946 0958
011 + 44 + 20 + 7946 0958
Drop the leading 0, add exit code + country code
From US to India
India domestic: 011 2345 6789 (Delhi)
011 + 91 + 11 + 2345 6789
Drop the leading 0, add exit code + country code
From US to Germany
Germany domestic: 030 1234567 (Berlin)
011 + 49 + 30 + 1234567
Drop the leading 0, add exit code + country code
Tip: On a mobile phone, you can always use + instead of 011. The + sign is universal and works from any country. Hold 0 on most phones to get +.
How to Format Phone Numbers (by Context)
| Context | Format | Example |
|---|---|---|
| Database storage | E.164 (no formatting) | +12125551234 |
| US display | Parentheses + dash | (212) 555-1234 |
| International display | + country code + spaces | +1 212 555 1234 |
| HTML tel: link | E.164 in href | <a href="tel:+12125551234"> |
| US dialing | 10 digits | 212-555-1234 |
Best practice: Always store phone numbers as strings (not integers) to preserve leading + and zeros. Normalize to E.164 on input, format for display on output.
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