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E.164

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E.164 International Phone Number Format

The international standard for phone numbers: a plus sign, country calling code, and national number, with no spaces, dashes, or parentheses.

Definition

E.164 is the international standard, defined by the ITU-T, for formatting phone numbers so they're unambiguous anywhere in the world. A number in this format always starts with a plus sign, followed directly by the country calling code and the national subscriber number, with no spaces, dashes, or parentheses in between, for example, +14155552671.

The format exists because locally formatted numbers only make sense within their own country. A number written as (415) 555-2671 tells a US caller everything they need, but a phone system in another country has no way to know it needs a +1 in front. E.164 fixes that by making the country code a mandatory, unambiguous part of the string itself, which is why it's the format required by SMS APIs, VoIP systems, and most phone number verification tools, including the Phone Number Validator.

Key Things to Know

  • Plus sign, then digits only: no spaces, hyphens, periods, or parentheses are allowed anywhere in a valid E.164 string, just + followed by up to 15 digits.
  • 15-digit maximum: the country code plus national number together can't exceed 15 digits under the ITU-T standard, though the vast majority of real numbers are 10-12 digits total.
  • Domestic trunk prefixes are dropped: a leading 0 used for local dialing in countries like the UK or India disappears in E.164, the country code makes it redundant.
  • It's a transport format, not a display format: applications typically store and transmit numbers in E.164, then reformat them for display using something like the US Phone Formatter.
  • No built-in check digit: unlike identifiers such as a VIN, E.164 has no checksum digit, validity checking relies on matching known country-code and length patterns rather than arithmetic.

Related Terms

Check DigitCheck Digit (Identifier Validation)

Frequently Asked Questions

What does an E.164 number actually look like?
It starts with a plus sign, followed immediately by the country calling code and the national subscriber number, with no spaces, dashes, or parentheses, for example +14155552671 for a US number or +919812345678 for an Indian one. Run a number through the [Phone Number Validator](/phone-number-validator/) to confirm it matches this shape.
How long can an E.164 number be?
The full number, including the country code but excluding the leading plus sign, can be at most 15 digits under the ITU-T standard. Most numbers are shorter than that; the 15-digit ceiling exists mainly to accommodate less common numbering plans.
Why do international systems insist on E.164 instead of local formats?
A locally formatted number like (415) 555-2671 is meaningless outside its home country, since it drops the country code a foreign system needs to route the call. E.164 removes that ambiguity by always including the country code, which is why SMS gateways, VoIP systems, and phone verification APIs require it.
Does E.164 include the leading zero some countries use domestically?
No, the leading trunk-prefix zero used for domestic dialing in countries like the UK or India is dropped in E.164 format, since the country code already establishes context. A UK number dialed domestically as 020 7946 0958 becomes +442079460958 in E.164.
Can I convert a locally formatted number to E.164 automatically?
Yes, if you know the source country, since the conversion is really just stripping local formatting characters, dropping any trunk prefix, and prepending the country code with a plus sign. The [US Phone Formatter](/us-phone-formatter/) handles the reverse direction, turning an E.164 or digit-only US number back into the familiar (415) 555-2671 display format.