E.164
The international standard format for phone numbers: +, country code, then the national number.
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E.164 is the ITU standard that defines how a phone number should be written for international use. The format is a leading plus sign, then the country calling code, then the national subscriber number, with a maximum of 15 digits and no spaces, dashes, or brackets.
A US number written locally as (415) 555-0132 becomes +14155550132 in E.164. The format is unambiguous, which is why nearly every telephony API, CRM, and messaging platform expects numbers in it.
Normalising a contact list to E.164 is usually the first step in any validation workflow. Inconsistent local formats are a common source of duplicate records and failed sends, because two spellings of the same number are treated as two different contacts.
Related terms and concepts
- NPA-NXX — The first six digits of a North American number: the area code plus the three-digit exchange prefix.
- List hygiene — Keeping a contact list accurate and current by removing or flagging unusable records.
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