The E.164 standard is the globally recognized format for structuring and formatting telephone numbers, including mobile numbers. Defined by the International Telecommunication Union (ITU), E.164 ensures that phone numbers are presented consistently across international borders, networks, and systems. This standard plays a critical role in telecommunications, helping mobile carriers, VoIP providers, and software applications handle phone numbers accurately and reliably.
1. Basic Structure of E.164
The E.164 format is designed to uniquely identify a phone number worldwide. It includes:
Country code: 1 to 3 digits (e.g., +1 for the USA, +44 for the UK, +91 for India)
National destination code (NDC): Often corresponds to area codes or mobile prefixes.
Subscriber number: The actual recent mobile phone number data user-assigned number.
Example (US number): +14155552671
Here,
+1 is the country code (USA),
415 is the area code,
5552671 is the subscriber number.
E.164 rules:
Must contain only digits (and a leading plus sign for display purposes).
Maximum of 15 digits total (excluding the "+" sign).
No spaces, hyphens, or parentheses are permitted in the strict format.
2. Why E.164 Is Important
E.164 provides a standardized format so that any telecom network or digital application can recognize and route a phone number correctly. This consistency is crucial for:
International dialing
Mobile carrier interoperability
Phone number verification in apps
Data integration across systems
Fraud detection and prevention
Without E.164, systems would struggle with inconsistent number formats, leading to failed calls, incorrect routing, or security issues.
3. E.164 in Practice
Most modern platforms and applications, such as WhatsApp, Twilio, and Google Contacts, use E.164 formatting to handle phone numbers. Here’s how:
Input validation: When users enter their number, systems often reformat it to E.164 automatically.
Storage: Databases typically store numbers in E.164 to avoid regional inconsistencies.
Contact syncing: Apps match phone numbers across devices and services using this format.
Many systems use libraries like Google’s libphonenumber to parse, validate, and convert numbers into E.164.
4. Examples of E.164 Formatted Numbers
Country Local Number E.164 Format
United States (415) 555-2671 +14155552671
UK 020 7946 0958 +442079460958
India 09876543210 +919876543210
Australia 0412 345 678 +61412345678
Note: Local formatting (with parentheses, spaces, or trunk codes like 0) is stripped in E.164.
5. E.164 vs. Other Formats
E.164 is different from:
National formats, which include local dialing rules and are country-specific.
RFC3966, which includes "tel:" URIs and may support extensions (e.g., tel:+14155552671;ext=123).
E.164 is the preferred format for telecom infrastructure and APIs, whereas other formats may be more human-friendly for display.