E.164 Phone Number Formatter

E.164 is the ITU-T standard that defines the international public telecommunication numbering plan. A number in E.164 format starts with a plus sign, followed by the country calling code and the national subscriber number, with no spaces, hyphens, parentheses or trunk prefix. For example, a US number written (415) 555-0132 becomes +14155550132.

Fifteen digits, excluding the leading plus sign. This is a hard limit set by ITU-T Recommendation E.164 and it includes the country calling code. The minimum is not fixed by the standard and varies by country, with some national numbers being as short as four or five digits.

The plus sign is the standard notation indicating that what follows is an international number rather than a national one, so numbers are normally written with it. The plus is not itself a digit and does not count toward the 15-digit limit. Some systems store numbers without it, which is a common source of matching failures when data moves between systems.

A trunk prefix is the digit or digits dialled before a national number when calling domestically, such as the 0 used in the UK and much of Europe or the 1 used in North America. It is a national dialling convention, not part of the subscriber number, so it is removed in E.164 format. Leaving it in is one of the most frequent formatting errors.

Caller-ID matching compares an incoming number against stored records. If numbers are stored in inconsistent formats, the comparison fails and the call does not match a contact, so screen pop and call logging silently stop working. Normalising everything to E.164 before connecting an integration resolves the large majority of these failures.

They are closely related but not identical in practice. International format often includes spaces or hyphens for readability, such as +44 20 7946 0958. E.164 is the strict machine-readable form with no separators at all: +442079460958. Use E.164 for storage and comparison, and a formatted version only for display.