International Phone Number Formats Explained: E.164, ITU Standards & More
If you've ever tried to dial an international number and been puzzled by how it should be written, you're not alone. Phone number formats can seem inconsistent and confusing — until you understand the international standards that underpin them. This guide breaks down everything you need to know.
What Is the E.164 Standard?
The most important international phone number format is E.164, defined by the International Telecommunication Union (ITU). It is the globally accepted standard for formatting phone numbers in telecommunications systems, APIs, and databases.
The E.164 format has three components:
- + — the international prefix symbol, replacing the international dialing access code
- Country code — 1 to 3 digits identifying the country
- Subscriber number — the national number (excluding the leading trunk digit like 0), up to 15 digits total
Example: A UK mobile number written locally as 07911 123456 becomes +44 7911 123456 in E.164 format. The leading 0 (trunk prefix) is dropped and replaced by the country code +44.
What Is a Trunk Prefix?
Many countries use a trunk prefix — typically 0 or 1 — when dialing within the country. This digit is part of the national format but is dropped when dialing internationally. Understanding this distinction prevents common dialing errors.
| Country | Trunk Prefix | Local Format | International (E.164) Format |
|---|---|---|---|
| United Kingdom | 0 | 07700 900123 | +44 7700 900123 |
| Germany | 0 | 0151 12345678 | +49 151 12345678 |
| India | 0 | 098765 43210 | +91 98765 43210 |
| Australia | 0 | 0412 345 678 | +61 412 345 678 |
| United States | 1 (country code = trunk) | (555) 123-4567 | +1 555 123 4567 |
International Dialing Access Codes
The + symbol in E.164 represents your country's international access code — the digits you dial to start an international call. This varies by country:
- 00 — used in most of Europe, Africa, the Middle East, and large parts of Asia
- 011 — used in the United States and Canada
- 0011 — used in Australia
Using the + symbol on a mobile phone automatically applies the correct access code for the country you're dialing from, making it the most universal approach.
Common Number Format Variations
Even within E.164, how numbers are visually displayed varies widely. You may see the same number written as:
- +1 (555) 123-4567
- +1-555-123-4567
- +15551234567
- +1 555 123 4567
All of these represent the same number. The spaces, dashes, and parentheses are purely visual formatting for human readability — they carry no technical meaning. When entering numbers into systems, databases, or APIs, always use the compact E.164 format without spaces or punctuation.
Special Number Categories and Their Formats
Beyond standard geographic and mobile numbers, countries also define formats for special-purpose numbers:
- Toll-free numbers: Typically begin with 800, 808, or similar (e.g., +1 800 xxx xxxx in the US)
- Premium rate numbers: Often start with 09x in the UK, 190x in Australia
- Short codes: 3–6 digit numbers used for SMS services; not dialable internationally
- Emergency services: 999 (UK), 911 (US), 112 (EU) — standardized but country-specific
Why Number Formats Matter for Lookup and Verification
When using phone lookup services, APIs, or validation tools, entering numbers in the correct E.164 format dramatically improves accuracy. Systems that rely on national formats can misidentify numbers or fail to match them against international databases. Always convert numbers to E.164 before querying a lookup service for the most reliable results.
Key Takeaway
International phone number formatting follows a clear standard: + country code + subscriber number, no trunk prefix, no spaces. Once you understand E.164 and how trunk prefixes work, formatting any number for international use becomes straightforward — wherever in the world it originates.