What Is E.164 Phone Number Format? The Definitive Guide with Examples

E.164 Defined: The International Phone Number Standard

E.164 is a numbering plan defined by the International Telecommunication Union (ITU-T) that specifies the format for international telephone numbers. It was originally published as ITU-T Recommendation E.164 and has been revised multiple times since its initial release. The standard provides a universal, unambiguous format for representing phone numbers that works across every country, carrier, and communications platform in the world.

The core rules of E.164 are simple. Every phone number must start with a + sign, followed by the country code (1 to 3 digits), followed by the subscriber number (the remaining digits). The total number of digits after the + sign must not exceed 15. No spaces, dashes, parentheses, or other formatting characters are allowed. The result is a clean, machine-readable string that can be routed to the correct destination anywhere on earth.

For example, the US phone number (555) 123-4567 becomes +15551234567 in E.164 format. The + sign indicates an international number, the 1 is the US country code, and the remaining 10 digits are the subscriber number. No ambiguity, no interpretation required, no formatting to strip.

Why E.164 Was Created

Before E.164, phone number formats were entirely country-specific. A number that was valid in the United States would not make sense in Germany or Japan. International dialing required knowing exit codes, trunk prefixes, and country-specific formatting rules. The ITU-T created E.164 to solve this fragmentation by providing a single format that unambiguously identifies any telephone subscriber on the global public switched telephone network (PSTN).

The standard became especially critical with the rise of mobile telephony and internet-based communications. When your application needs to send an SMS, make a VoIP call, or verify a phone number, it needs to know exactly which country and subscriber it is reaching. E.164 provides that certainty. Without it, a number like 07700900000 could be a UK mobile number, or it could be interpreted as a US number with a missing area code, or it could be invalid entirely. With E.164, +447700900000 is unambiguously a UK mobile number.

E.164 Structure Breakdown

Every E.164 number follows this exact structure:

E.164 Examples for 10 Countries

The following table shows how local phone number formats convert to E.164 for the 10 most commonly encountered countries in business data. Note how each country has different local formatting conventions, but the E.164 output is always consistent.

Notice several important patterns. The US and Canada share country code +1, which is part of the North American Numbering Plan (NANP). The UK, Australia, and Japan all have trunk prefixes (leading 0) in their local formats that must be removed when converting to E.164. Germany, France, and Brazil have variable-length subscriber numbers. Mexico recently simplified its numbering by eliminating the mobile prefix "1" that was previously required after the country code.

Which Services Require E.164 Format?

Nearly every major communications API and CRM platform either requires or strongly recommends E.164 format. Here are the most common services and their E.164 requirements:

• Twilio: E.164 required for all API calls. Numbers without the + prefix and country code will be rejected.
• AWS SNS: E.164 required for SMS publishing. The PhoneNumber parameter must be in E.164 format.
• MessageBird: E.164 required for all messaging APIs. Their documentation explicitly states: "Phone numbers should always be in E.164 format."
• Vonage (Nexmo): E.164 required. Numbers must include country code without the + prefix (Vonage uses their own slight variant but based on E.164).
• Bandwidth: E.164 required for all voice and messaging APIs. The + prefix is mandatory.
• Plivo: E.164 required. Their number formatting guide explicitly references the ITU-T recommendation.
• HubSpot: E.164 recommended for contact phone properties to ensure correct international dialing.
• Salesforce: E.164 recommended for Phone fields, required for telephony integrations.
• Mailchimp: E.164 with country code required for SMS campaign features.

How to Identify If a Number Is E.164 Compliant

A phone number is E.164 compliant if and only if it meets all of the following criteria:

1. It starts with a + sign.
2. The + is immediately followed by a valid country code (1 to 3 digits).
3. The country code is followed by the subscriber number with no trunk prefix.
4. The total number of digits (after the +) does not exceed 15.
5. It contains no spaces, dashes, parentheses, dots, or other non-numeric characters (except the leading +).

A quick regex test for E.164 compliance is: ^\+[1-9]\d{1,14}$. This matches a + sign, followed by a non-zero digit (country codes never start with 0), followed by 1 to 14 additional digits (for a total of 2 to 15 digits). If your phone number matches this pattern, it is structurally E.164 compliant. However, structural compliance does not guarantee the number is valid. The country code must correspond to a real country, and the subscriber number must have the correct length for that country.

Common E.164 Formatting Mistakes

Missing the + Prefix

The most common mistake is omitting the + sign. The number 15551234567 looks like it might be E.164 (it has the country code and the right number of digits), but without the + prefix, many APIs will reject it or misinterpret it. Some services like Vonage accept numbers without the + sign, but most strictly require it. Always include the +.

Missing the Country Code

A US number stored as +5551234567 is missing the country code. The correct E.164 format is +15551234567 where 1 is the US country code. Similarly, a UK number stored as +7700900000 is missing the 44 country code. This mistake often happens when converting from local format and forgetting to prepend the country code after removing the trunk prefix.

Including the Trunk Prefix

Many countries use a trunk prefix (usually 0) for domestic dialing. When converting to E.164, this prefix must be removed. A UK number dialed locally as 07700900000 has a trunk prefix of 0. The E.164 format drops the 0 and adds the country code: +447700900000. Keeping the 0 would produce +4407700900000, which is invalid. This is the most common conversion error for UK, Australian, German, French, and Japanese numbers.

Including Spaces, Dashes, or Parentheses

E.164 numbers must contain only the + sign and digits. The number +1 (555) 123-4567 is not E.164 compliant even though it has the country code and + prefix. Formatting characters must be stripped entirely. Many APIs will reject numbers that contain any non-numeric character other than the leading +.

How to Convert Phone Numbers to E.164 in Bulk

If you have a CSV with hundreds or thousands of phone numbers in mixed formats, manually converting each one is impractical. NoSheet's phone formatter tool converts any input format to E.164 automatically. Upload your CSV, select the phone column, choose the default country code for numbers that do not have one, and every number in the column is converted in seconds.

The tool handles all of the edge cases described above: stripping trunk prefixes, adding country codes, removing formatting characters, and validating the result against E.164 rules. Numbers that cannot be parsed (because they are too short, contain letters, or are otherwise invalid) are flagged for manual review rather than silently corrupted.

For step-by-step instructions, see our guide on converting phone numbers to E.164 or our tutorial on formatting phone numbers in bulk.

Frequently Asked Questions

Is E.164 the same as international format?

E.164 is one specific international format, but "international format" is a broader term that can include formatted versions with spaces and dashes. When someone says "international format," they might mean +1 555-123-4567 (with dashes). E.164 specifically means +15551234567 (no formatting characters). For API and database purposes, always use E.164.

Can E.164 numbers have extensions?

No. E.164 represents the dialable portion of a phone number only. Extensions are not part of the E.164 standard. If you need to store extensions, keep them in a separate field. Appending an extension to an E.164 number (like +15551234567x200) violates the standard and will cause parsing failures in most APIs.

Do I need E.164 for domestic-only use?

Technically no, but practically yes. Even if your business only operates in one country, storing numbers in E.164 format prevents issues when you integrate with third-party services, switch telephony providers, or eventually expand internationally. It is the canonical format and converting to it early saves significant cleanup effort later.

What is the maximum length of an E.164 number?

15 digits, not counting the + prefix. In practice, most numbers are between 10 and 13 digits. US/Canada numbers are always 11 digits (1 + 10 subscriber digits). UK mobile numbers are 12 digits (44 + 10 subscriber digits). Some country codes are 3 digits long (e.g., +880 for Bangladesh), which still allows up to 12 subscriber digits.

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