Frequently Asked Questions
E.164 is an international standard defining the format of phone numbers for global communication. It ensures consistent call routing and compatibility between different countries and network operators. This format is essential for accurate identification and connection with phone numbers worldwide, supporting various communication technologies like mobile, IP telephony, and international roaming.
E.164 validation involves a multi-layered approach. Start with basic format validation using a regex to check the structure. Then, perform country-specific checks using a database of regional rules and restrictions. Finally, validate the total number length, accounting for variable NDC lengths within certain countries. This comprehensive strategy helps ensure data integrity.
E.164 is crucial for seamless international communication by providing a standardized format for phone numbers. This facilitates consistent call routing, network interoperability, and reliable access to emergency services. It supports essential features such as mobile number portability and international roaming capabilities, accommodating advancements in communication technologies.
For international calls, use the plus sign (+) followed by the country code, national destination code, and subscriber number. For example, +1-415-555-0123. This format ensures correct routing across global networks. Remember to store phone numbers in the pure E.164 format without any formatting characters for consistency.
The maximum length of an E.164 number is 15 digits. This includes the country code (1-3 digits), national destination code (typically 2-4 digits), and subscriber number. The minimum length is the country code length plus at least one additional digit. These length constraints are essential for global compatibility.
To convert local numbers to E.164, first remove any non-digit characters like spaces, hyphens, or parentheses. Then, prepend the appropriate country code. For instance, a US number (415) 555-0123 would become +14155550123. This ensures consistent handling regardless of the original input format.
Consider using libphonenumber-js when building web applications that require E.164 validation and formatting, especially if minimizing bundle size is a priority. It offers a smaller footprint than Google's full phone number library while providing essential features for accurate handling of international phone numbers.
An E.164 number comprises three key components: the Country Code (CC), National Destination Code (NDC), and Subscriber Number (SN). The CC identifies the country, the NDC specifies a region within the country, and the SN uniquely identifies the individual subscriber. These components are crucial for correct routing and identification of phone numbers.
E.164 supports mobile number portability, allowing users to keep their numbers when switching carriers. This ensures continuous connectivity and prevents disruption of communication services. This feature is managed within the NDC framework within each country or region.
Yes, JavaScript libraries like phone
and libphonenumber-js
simplify E.164 validation. These libraries provide efficient and accurate methods to check phone number compliance with international standards, handling diverse input formats and edge cases.
Initially introduced in 1984 for ISDN, E.164 has evolved to support modern telecommunications, including IP telephony, mobile number portability, and emergency services. Its maximum length was expanded from twelve to fifteen digits in 1997. This continuous evolution maintains its relevance in the changing communication landscape.
When dealing with invalid country codes, cross-check them against the official ITU-T list. Also, verify the number's length complies with country-specific rules. Regularly updating your country code database is vital, as these codes can change, potentially invalidating existing data.
Storing E.164 numbers without formatting, such as spaces or hyphens, ensures data consistency and simplifies processing. This 'pure' format facilitates accurate comparisons, validation, and integration with various systems and databases. Always use local formatting only for display purposes.
E.164 Phone Number Format: Complete Guide to Validation & Implementation (2025)
Learn how to validate, format, and convert phone numbers to E.164 format—the international standard for telecommunications. This guide covers E.164 format examples, regex validation patterns, JavaScript implementation with libphonenumber-js, conversion tools, and integration with Twilio and SMS systems for global phone number handling.
What is E.164 Phone Number Format?
E.164 is the international telecommunication standard that defines the format for phone numbers worldwide. The ITU-T (International Telecommunication Union) establishes specifications for structuring phone numbers to enable global dialing across all networks and countries. The official ITU-T Recommendation E.164, titled "The international public telecommunication numbering plan," provides these specifications (ITU-T E.164, 2010).
An E.164 phone number has a maximum of 15 digits and follows this structure:
E.164 Format Example: +14155550123 (where +1 is USA, 415 is San Francisco area code, 5550123 is the subscriber number)
E.164 forms the foundation of global telecommunications, ensuring consistent call routing and interoperability between countries and network operators. It's the universal language for phone numbers, allowing systems to correctly identify and connect calls across all countries and carriers. This standardized format is essential for SMS delivery, international calling, VoIP services, and two-factor authentication systems.
Historical Context and Evolution: From ISDN to the Modern Era
First published in 1988 as the "Numbering Plan for the ISDN Era," E.164 has continuously evolved to keep pace with advancements in telecommunications. The standard expanded to accommodate growing global demand for phone numbers. The most substantial revision is E.164 (11/2010), approved November 18, 2010, with periodic amendments continuing through ITU Operational Bulletins (latest amendments published July 2020, Bulletin No. 1199) to address the complexities of modern communication, including:
E.164 is not a static standard but a dynamic framework adapting to the ever-changing landscape of global communication, including emerging technologies like virtual phone numbers and cloud telephony platforms.
E.164 Format Specifications: Understanding Phone Number Structure
The E.164 phone number structure consists of precisely defined components that enable global interoperability. Understanding this structure is essential for accurate validation and implementation across international telecommunications systems.
E.164 Number Structure: The Three Essential Components
An E.164 number consists of three key components, each playing a crucial role in accurate routing:
Country Code (CC): This 1–3 digit prefix identifies the country. For example, +1 is for North America, +44 for the UK, and +86 for China. The ITU-T assigns these codes (ITU-T E.164, 2010).
National Destination Code (NDC): This variable-length code identifies a specific geographic area, mobile network, or service within a country. National authorities manage these codes. NDC lengths vary both between and within countries depending on the numbering plan design.
Subscriber Number (SN): This is the remaining portion of the number, uniquely identifying the subscriber within the NDC zone. The combined length of NDC and SN cannot exceed 12 digits. Together, the NDC and SN form the National Significant Number.
Understanding these components is crucial when parsing and validating E.164 numbers.
E.164 Format Requirements and Validation Rules
E.164 numbers must adhere to strict formatting rules to ensure global compatibility:
1. Character Set
Only digits 0–9 are allowed per ITU-T E.164. A plus (+) prefix indicates international format for display but should be omitted from stored data. No spaces, hyphens, or other separators are allowed in the canonical format. This ensures consistency and simplifies processing.
2. Length Constraints
The minimum length is the CC length plus one digit. The maximum total length is 15 digits (comprising 1–3 digit country code plus up to 12 digits for the national number). Country-specific minimum lengths also apply, adding another layer of complexity to validation.
3. Structural Rules
Use a regular expression to enforce the basic E.164 format:
^\+[1-9]\d{1,14}$
^[1-9]\d{1,14}$
Important Note: This regex validates basic structure but does not verify country-specific rules or whether the number actually exists. For production validation, use specialized libraries like libphonenumber-js that maintain comprehensive country-specific rulesets.
How to Validate E.164 Phone Numbers: Implementation Guide
Implementing robust E.164 phone number validation requires a multi-layered approach that combines format checking, country-specific validation, and length verification. This section provides step-by-step implementation guidance for building reliable phone number validation into your applications.
Phone Number Validation Strategy: Multi-Layered Approach
A robust validation strategy incorporates multiple layers to ensure accuracy:
/^\+[1-9]\d{1,14}$/
Implementation Example:
How to Convert Phone Numbers to E.164 Format
Converting local or national phone numbers to E.164 format is a common requirement when processing user input. Follow these steps for accurate conversion:
Conversion Process:
E.164 Conversion Examples by Country:
Code Example:
Common Edge Cases in Phone Number Validation
Real-world phone number validation requires handling several edge cases:
1. International Display Format
For user-friendliness, format numbers with appropriate separators for display (e.g., +1-415-555-0123). Store numbers in canonical E.164 format internally.
2. Multiple Input Formats
Users enter phone numbers inconsistently – with dashes, parentheses, spaces, or no formatting at all. Normalize all inputs before validation to ensure consistent processing.
3. Extension Numbers
Phone extensions (e.g., +1-415-555-0123 ext. 456) are not part of the E.164 standard. Store extensions separately:
4. Special Service Numbers
Handle these number types separately as they may not follow standard validation rules:
5. Vanity Numbers
Convert alpha-numeric vanity numbers (e.g., 1-800-FLOWERS) to numeric format:
Best Practices: Ensuring Data Integrity and User Experience
Implement E.164 effectively by following these best practices:
1. Storage
Always store phone numbers in the pure E.164 format, removing all formatting characters. This ensures data consistency and simplifies processing. E.164 numbers are limited to 15 digits, making storage requirements predictable. Use appropriate database field types:
2. Display
Use local formatting conventions for user interfaces to enhance readability. However, always maintain the E.164 format internally for system operations. Consider cultural formatting preferences to provide the best user experience.
3. Validation
Implement progressive validation, checking the number at both input and processing stages. Use established libraries for complex validation logic. This minimizes errors and improves data quality.
4. Security & Privacy
Treat phone numbers as Personally Identifiable Information (PII). Implement these security measures:
Implementation Example:
Key Management:
Privacy Compliance:
5. API Rate Limiting
When using validation services or carrier lookup APIs, implement rate limiting and caching to prevent abuse and reduce costs. Consider implementing exponential backoff for failed validation attempts.
Caching Strategy:
Troubleshooting E.164 Phone Number Validation: Common Issues & Solutions
When implementing E.164 validation_ developers frequently encounter specific issues that can cause validation failures or incorrect phone number handling. Here are the most common problems and their solutions:
Issue 1: Invalid Country Codes
Problem: Numbers fail validation due to incorrect or outdated country codes.
Solutions:
Monitoring ITU Changes:
Subscribe to ITU Operational Bulletins for official notifications of numbering plan changes. Recent examples include:
Issue 2: Format Inconsistencies in User Input
Problem: Users submit phone numbers in various formats (with spaces_ hyphens_ parentheses)_ causing validation failures.
Solutions:
Implement progressive validation at both input and processing stages to catch errors early.
Issue 3: Regional Numbering Variations
Problem: Variable NDC lengths and special number formats within countries cause validation errors.
Solutions:
Special Number Ranges by Type:
Issue 4: Failed Call Routing or Integration
Problem: Non-E.164 formatted numbers cause failed API calls_ unsuccessful contact synchronization_ or routing issues.
Solutions:
Debugging Checklist:
Best E.164 Phone Number Validation Libraries (2025)
Implementing E.164 validation from scratch is complex due to country-specific rules and frequent numbering plan updates. These actively maintained JavaScript libraries simplify validation and formatting while ensuring compliance with current international standards.
Library Comparison Overview
When to choose which library:
Using the
phone
LibraryThe
phone
npm package (v3.1.67, October 2025) provides robust E.164 standardization and validation for mobile phone numbers. It handles diverse input formats and ensures compliance with international standards. Note: This library focuses specifically on mobile number formats.Installation and Setup
Usage Example
Using
libphonenumber-js
libphonenumber-js
is a lightweight implementation of Google's phone number library, optimized for web applications. It's based on Google's canonical libphonenumber but offers significantly better performance for JavaScript environments.Installation and Setup
Usage Example
Key Features
Current Version: libphonenumber-js v1.12.23 (October 2025)
libphonenumber-js
is ideal for web applications where bundle size is critical. For server-side applications where bundle size is less critical, Google's originallibphonenumber
implementation (available asgoogle-libphonenumber
v3.2.43 on npm) provides the most comprehensive validation.Metadata Update Strategy:
Keep your validation library current to handle new numbering plans and country code changes:
Schedule automated updates quarterly or monitor the libphonenumber-js release notes for critical metadata updates.
Modern Considerations: E.164 in Today's Digital Landscape
As communication technology evolves, several modern considerations have emerged for E.164 implementation:
Virtual Phone Numbers and VoIP
Cloud telephony services and VoIP providers have introduced virtual phone numbers that follow E.164 formatting but may not correspond to traditional geographic locations. RFC 3824 defines procedures for using E.164 numbers with the Session Initiation Protocol (SIP), the foundation of modern VoIP systems. When validating these numbers:
ENUM Lookup Implementation:
Carrier Lookup Services:
Use carrier lookup APIs to identify number types and routing:
eSIM and Digital-First Numbers
The rise of eSIM technology has created new patterns in phone number provisioning. GSMA specifications govern eSIM remote provisioning: SGP.22 v2.6 (October 2024) for consumer devices and SGP.32 for IoT devices. Key considerations:
Privacy and Data Protection
Modern privacy regulations require careful handling of phone numbers:
GDPR Compliance (European Union)
CCPA Compliance (California)
Implementation Considerations
Pseudonymization Techniques:
Two-Factor Authentication (2FA) Considerations
When using phone numbers for 2FA:
Best Practices:
Security Concerns:
SIM Swap Detection:
Voice vs SMS 2FA Delivery:
Frequently Asked Questions About E.164 Format
What is E.164 format for phone numbers?
E.164 format is the ITU-T international standard for structuring phone numbers, consisting of a country code (1–3 digits), national destination code, and subscriber number, with a maximum total length of 15 digits. The format starts with a + symbol followed by digits only, for example: +14155550123. E.164 ensures global interoperability for telecommunications systems.
How do I convert a phone number to E.164 format?
To convert to E.164 format: (1) Remove all formatting characters (spaces, hyphens, parentheses), (2) Remove leading zeros if present, (3) Add the country code prefix with +, (4) Verify the number contains only digits and is 15 digits or fewer. Example: (415) 555-0123 becomes +14155550123. Use validation libraries like libphonenumber-js for automated conversion.
What is the regex for E.164 validation?
The basic E.164 regex pattern is:
^\+[1-9]\d{1,14}$
This matches a + symbol, followed by a non-zero digit, then 1–14 additional digits (total 2–15 digits after the +). Note: This validates structure only and does not verify country-specific rules or number validity.
Why is E.164 format important for international phone numbers?
E.164 format ensures global interoperability for telecommunications, enabling consistent phone number parsing, validation, and call routing across different countries, carriers, and systems. Without E.164 standardization, international calls would fail, SMS messages wouldn't deliver, and VoIP services couldn't properly route communications. The format eliminates ambiguity in phone number interpretation across 195+ country codes.
Can E.164 format include country codes?
Yes, E.164 format always includes the country code as the first 1–3 digits after the + symbol. The country code is mandatory in E.164 format to enable international dialing.
What's the difference between E.164 and national phone number formats?
E.164 is the international format that always includes the country code (e.g., +14155550123), while national formats are country-specific and omit the country code (e.g., (415) 555-0123 in the USA). National formats often include local formatting conventions like parentheses, hyphens, and spaces for readability. E.164 standardization enables global compatibility and unambiguous number identification across borders, making it essential for international telecommunications, SMS gateways, and VoIP systems.
Is the + symbol required in E.164 format?
The + symbol is used for display purposes to indicate the international format, but the stored E.164 format should contain only digits. The + helps distinguish international numbers from local formatting.
How do I validate E.164 phone numbers in JavaScript?
The most reliable method is using specialized validation libraries like libphonenumber-js or phone npm package, which maintain current country-specific rules:
For basic format validation, use regex:
/^\+[1-9]\d{1,14}$/
, but note this doesn't verify country-specific rules or actual number validity.How do I use E.164 format with Twilio for SMS?
Twilio requires phone numbers in E.164 format for SMS and voice calls. Convert numbers using libphonenumber-js before sending:
Learn more about Twilio E.164 requirements for SMS delivery.
What is the minimum length for E.164 phone numbers?
The E.164 format minimum length varies by country but typically ranges from 8 to 15 digits total (including country code). For example, US numbers are always 11 digits (+1 followed by 10 digits), while some countries like the Solomon Islands may have shorter numbers. Use validation libraries to check country-specific minimum lengths.
Conclusion: Implementing E.164 Phone Number Validation
By understanding and implementing the E.164 international phone number format, you ensure accurate and reliable global communication for your applications. This comprehensive guide has equipped you with:
Whether you're building authentication systems, international calling features, or SMS messaging platforms, proper E.164 implementation is critical for global interoperability. Stay updated on ITU-T revisions and maintain your country code databases for optimal performance.
Ready to implement E.164 validation in your application? Start with libphonenumber-js for lightweight web applications or Google's libphonenumber for comprehensive server-side validation. Both libraries handle the complexity of country-specific rules, allowing you to focus on building great user experiences with reliable international phone number support.