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E.164

published · September 10, 2026

E.164 is the ITU-T standard that gives every phone number one unambiguous international form: a plus sign, a country calling code, and at most fifteen digits.

E.164 is the ITU-T standard that gives every phone number one unambiguous international form: a plus sign, a country calling code, and at most fifteen digits in total, with no spaces, brackets or dashes. +14155550142 is E.164; (415) 555-0142 is the same number written for a person.

What Spaw answers

e164 is the canonical form and the field to store. Three others carry the same number written differently: national for display inside its own country, international for display across borders, and rfc3966 as a tel: URI for a dial link.

Why the country parameter exists

Every region's calling code, with an example number in each form, is on its page under phone facts by country.

E.164 is unambiguous only when the calling code is present. A number typed without one — 4155550142, or a national form beginning with a trunk 0 — could belong to several countries, so a lookup needs country to know which numbering plan to read it against. Without one the answer is missing_country, which is free.

An API key can carry a default country, applied only when the request body names none at all; an explicit country: null still means "read it from the calling code".

Related

markdown version: /glossary/e164.md

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More glossary

  • Area-code overlay

    An area-code overlay is a new area code added over the same area as an existing one, instead of splitting it, so neighbours can hold different codes and local calls need ten digits.

  • Calling window

    A calling window is the span of local hours a sender contacts people in. Spaw answers in_call_window from the number's time zones: clock arithmetic, not compliance advice.

  • Fictional number

    A fictional number sits in a range kept out of service for films, TV and other fiction: 555-0100 to 555-0199 in North America, and ranges Ofcom, ARCEP, ACMA and ComReg reserve elsewhere.

  • International (exit) prefix

    An international prefix is what is dialled to leave a country before the calling code: 00 in most of the world, 011 in North America. Spaw reads it and suggests a fix in did_you_mean.

  • International network number

    An international network number sits under a calling code the ITU gives a global service rather than a country, such as +870, +881, +882 or +883, so its country is null.

  • Live carrier check (HLR lookup)

    A live carrier check asks the mobile networks, at the moment of the lookup, whether a number is in service, which network serves it and whether it is roaming. On Spaw it is not enabled.

  • Number pooling (thousands-blocks)

    Number pooling splits a North American central office code into ten blocks of a thousand numbers, each assigned to a carrier separately, so one code can hold several carriers' numbers.

  • Number portability

    Number portability lets a subscriber keep a phone number when changing carrier. The number's block stays listed under the carrier it was issued to, so block data names the original holder.