E.164 is the international standard for phone number formatting, defined by the ITU (International Telecommunication Union). It specifies that every phone number in the world can be written as a single string starting with `+`, followed by a 1-3 digit country code, followed by the subscriber number, with no spaces or punctuation, up to a maximum of 15 digits total. Example: `+15551234567` for the US, `+447911123456` for the UK.

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

The maximum length of an E.164 phone number is 15 digits, including the country code. The shortest country codes are 1 digit (such as `+1` for North America or `+7` for Russia), the longest are 3 digits (such as `+998` for Uzbekistan). Anything longer than 15 digits is invalid under the E.164 standard. The `+` sign itself is not counted as a digit.

What is the international phone number format?

The international phone number format includes the country code prefixed with `+`, then the area code without the trunk prefix, then the local number — for example `+1 555 123 4567` (US) or `+44 7911 123456` (UK). It is the human-readable version of E.164: the same digits, but with spaces or hyphens for readability. International format is what you display to humans; E.164 is what you store in databases and APIs.

What is the difference between E.164 and international format?

E.164 and international format describe the same digits — the only difference is presentation. E.164 (`+15551234567`) has no spaces or punctuation and is intended for machines: databases, APIs, WhatsApp wa.me links, SMS gateways. International format (`+1 555 123 4567`) adds spaces or hyphens for human readability. Both start with `+` and the country code, and neither includes the trunk prefix used for domestic dialling.

What is the difference between E.164 and E.123?

E.164 and E.123 are sibling ITU recommendations that work together. E.164 defines the **structure** of a phone number — country code plus subscriber number, max 15 digits. E.123 defines the **notation** for writing phone numbers down — how to use spaces, parentheses, and the `+` symbol when displaying numbers to humans. In practice, you store numbers in E.164 (`+15551234567`) and display them using E.123 conventions (`+1 555 123 4567`).

How do I convert a phone number to E.164?

To convert a phone number to E.164: (1) identify the country, (2) look up the country code (e.g. 1 for US, 44 for UK, 49 for Germany), (3) drop any trunk prefix used for domestic dialling — usually the leading `0` (Italy is a notable exception where the leading 0 is kept), (4) combine `+` + country code + subscriber number with no spaces or punctuation. The free [NumSwift E.164 converter](https://www.numswift.com/e164-format-converter) does this automatically for any country and also outputs international, national, and RFC 3966 (tel:) formats.

Why is E.164 the international phone number standard?

E.164 is the standard because it is unambiguous and globally unique — every valid phone number on the planet can be written in exactly one E.164 form. This makes it the only safe format for storing numbers in a database, sending SMS through APIs like Twilio or MessageBird, generating WhatsApp wa.me links, or routing calls through telephony networks. Local and national formats are ambiguous outside their own country, but E.164 always identifies a specific subscriber worldwide.

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Phone Number ManagementJanuary 8, 20257 min read

Phone Number Formats Explained: E.164, International, National & Local (2026)

E.164 Format Converter

Convert any phone number to E.164, international, national or tel: format

Default country (used when the number has no “+”): change it in the country selector at the top of the page.

Privacy: conversion runs entirely in your browser using libphonenumber-js. Numbers never leave your device. Feedback?

The same phone number can be written in half a dozen different ways. A US number might appear as:

555-123-4567
(555) 123-4567
+1 555 123 4567
15551234567
+15551234567
1 (555) 123-4567

All of these represent the same number. But depending on where you use them — a phone call, a WhatsApp message, an API, a database — only certain formats will work.

This guide covers all four standard phone number formats — local, national, international, and E.164 — explains the international phone number standard set by the ITU, and shows how to convert between them with confidence.

What is E.164?

E.164 is the international standard for phone number formatting, defined by the ITU (International Telecommunication Union). Every phone number in the world can be written in exactly one E.164 form — making it the only unambiguous way to identify a subscriber globally.

An E.164 phone number consists of:

A leading + sign
A country code (1–3 digits)
A subscriber number (the rest, up to a total of 15 digits maximum)
No spaces, no dashes, no parentheses

+15551234567       ← US
+447911123456      ← UK
+493012345678      ← Germany
+819012345678      ← Japan

E.164 is what databases, SMS gateways, WhatsApp wa.me links, and CRM systems use internally. If you remember one rule: store phone numbers in E.164, always. Everything else can be derived from it.

Local Format

The number as dialed within the same area or city. No area code, no country code.

123-4567

When it works: Calling from a landline within the same area code. Increasingly rare as mobile phones always require at least the area code.

When it doesn't work: Anywhere outside the immediate local area. Useless for digital systems, WhatsApp, or international communication.

National Format

The full number as dialed within the same country. Includes the area code (and trunk prefix, if applicable) but no country code.

(555) 123-4567       ← US national
0555 123 4567        ← UK national (0 is the trunk prefix)
030 12345678         ← Germany national

When it works: Making calls or sending SMS within the same country. Most people's default way of writing phone numbers.

When it doesn't work: International calls, WhatsApp (which needs the international format), APIs, and databases that store numbers from multiple countries.

International Format

The full number formatted for international dialing. Includes the country code and drops the trunk prefix.

+1 555 123 4567      ← US
+44 555 123 4567     ← UK (trunk prefix 0 removed)
+49 30 12345678      ← Germany (trunk prefix 0 removed)

The + sign at the beginning means "replace with your country's international dialing prefix" (00 in most of Europe, 011 in the US).

When it works: International phone calls, displaying numbers for a global audience, and as a human-readable version of E.164.

E.164 Rules and When to Use It

We covered the basics in What is E.164? above. Here are the precise rules and the situations where E.164 is the only format that works.

Rules:

Starts with +
Country code (1–3 digits)
Subscriber number (without the trunk prefix)
No spaces, dashes, parentheses, or other formatting
Maximum 15 digits total (including the country code)

When to use E.164:

Storing phone numbers in a database
WhatsApp wa.me links (without the +)
SMS APIs (Twilio, MessageBird, Vonage, etc.)
Any system that processes phone numbers programmatically
CRMs and contact management systems

E.164 is the canonical format. Every other format can be derived from it, but converting back to E.164 from a local or national format requires knowing the country. If you need to convert numbers between formats, having the country context is essential.

E.164 vs E.123

E.164 and E.123 are sibling ITU recommendations that often get confused. They solve different problems and work together:

| Standard | What it defines | Example | | --------- | -------------------- | ---------------------------------------- | | E.164 | Number structure | +15551234567 — digits and country code | | E.123 | Written notation | +1 555 123 4567 — spacing and the + |

E.164 is the data format. It says which digit sequences are valid phone numbers worldwide. There is exactly one E.164 representation per number.
E.123 is the display format. It says how to write a phone number on a business card, in a contact field, or on a website. It defines spacing, optional parentheses around area codes, and the + symbol convention.

In practice, you store phone numbers as E.164 and render them using E.123 notation. Most phone number libraries (Google's libphonenumber, for example) provide a formatInternational() method that converts E.164 to E.123-style display.

How the Formats Relate

For the UK number 07911 123456:

| Format | Value | Notes | | ------------- | --------------- | ---------------------------------------- | | Local | 123456 | Just the subscriber number | | National | 07911 123456 | With trunk prefix (0) | | International | +44 7911 123456 | Trunk prefix removed, country code added | | E.164 | +447911123456 | No formatting, just digits and + |

For the US number (555) 123-4567:

| Format | Value | Notes | | ------------- | --------------- | ---------------------------------------------- | | Local | 123-4567 | Just the local number | | National | (555) 123-4567 | With area code | | International | +1 555 123 4567 | Country code added (no trunk prefix to remove) | | E.164 | +15551234567 | No formatting, just digits and + |

The Trunk Prefix Problem

The trunk prefix is the digit (usually 0) you dial before a national number for domestic calls. It's not part of the actual phone number — it's a routing instruction for the phone network.

The rule: Drop the trunk prefix when converting to international or E.164 format.

The exceptions:

US/Canada: No trunk prefix exists. The number is the same in national and international format (just add +1).
Italy: The leading 0 is part of the number and must be kept in international format.
Some countries use a different trunk prefix: Russia uses 8, some countries use other digits.

This is where most formatting mistakes happen. If you're unsure, NumSwift handles the conversion automatically — paste any number in any format and it outputs the correct international version. For a deeper dive into trunk prefixes and dialing conventions, see our guide on formatting numbers for international calling.

Why This Matters for WhatsApp

WhatsApp uses E.164 format internally. When you create a wa.me link:

https://wa.me/447911123456

That's E.164 without the +. If you include the trunk prefix or use the wrong country code, the link won't work — or worse, it'll open a chat with the wrong person.

Why This Matters for Developers

If you're building an application that handles phone numbers:

Store in E.164. Always. It's unambiguous and globally unique.
Display in international format. Add spaces and formatting for readability. A phone number formatter can handle this conversion consistently.
Accept any format. Users will enter numbers however they're used to. Parse and convert to E.164 on input. Consider adding validation to catch invalid numbers early.
Use a library. Don't write your own phone number parser — use Google's libphonenumber or an equivalent. Phone number formatting rules are complex and change regularly.

Converting Between Formats

Manual Conversion

To convert a national number to E.164:

Identify the country
Find the country code
Remove the trunk prefix (if applicable)
Combine: + + country code + number (no spaces)

Automatic Conversion

The free E.164 format converter converts any phone number to E.164, international (E.123), national, and RFC 3966 (tel:) formats with one-click copy. Paste a single number or a full list — everything runs in your browser using libphonenumber-js. For extracting numbers from blocks of unstructured text instead of converting a single value, use the main NumSwift extractor.

For a complete list of country codes and their formatting rules, see the International Phone Number Format Guide.

Related Guides

E.164 format converter — free online tool that converts any phone number to E.164, international, national, and RFC 3966 (tel:) formats
How to format any phone number for international calling — step-by-step instructions for exit codes, trunk prefixes, and the + shortcut
Phone number validation: how to check if a number is real — go beyond formatting to verify whether a number actually exists
International phone number format and country codes — complete reference for 200+ country codes and dialing conventions
Phone Number Formats by Country — Phone number formats for 30+ countries with examples and formatting tables

Bottom Line

Local format is for calling your neighbor. National format is how most people write numbers. International format is for human-readable cross-border communication. E.164 is for machines — databases, APIs, WhatsApp links, and any system that needs an unambiguous phone number.

When in doubt, convert to E.164. And when you don't want to figure out the conversion yourself, NumSwift does it in one paste.