E.164

International (ITU-T) · also called international number format

The ITU standard for international telephone number format — e.g. +1 626 555 0100 — with country code and up to 15 digits.

E.164 is the ITU-T recommendation that defines the international public telecommunication numbering plan. An E.164 number consists of a country calling code followed by a national number, up to 15 digits total, conventionally written with a leading "+". For the NANP, the country code is 1, so a number is written +1 NPA NXX XXXX.

E.164 is the canonical, globally unambiguous form of a phone number and the format most systems store and exchange.

A number is country code + area code (NPA) + prefix (NXX) + a four-digit line number. The first digit of the four-digit line number — the seventh digit of the 10-digit national number, not counting the country code +1 — marks which pooled thousands-block of 1,000 numbers it belongs to.

Common misconception.

E.164 is a format standard, not a directory. It specifies how numbers are written and structured internationally; it does not assign or look up numbers.