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E.164 International Phone Number Format

Updated 2026-09-30 · By the ZuteSIP team (ZuteSIP Inc.)

Short answer: E.164 is the ITU-T recommendation that defines the international public telephone numbering plan, including the format used to write any number worldwide: a plus sign, the country code and the national number, with no spaces or leading trunk zero, up to 15 digits in total. For example, a UK number written 020 7946 0000 becomes +442079460000.

Apps, SIP systems and verification services often expect E.164 because it identifies a number uniquely wherever it is dialled from.

Definition

ITU-T Recommendation E.164 assigns country codes and sets the maximum length of an international number at 15 digits. The plus sign stands for whatever international dialling prefix applies where you are.

How it works

National formatE.164
(415) 555-0123 (US)+14155550123
020 7946 0000 (UK)+442079460000
030 123456 (Germany)+4930123456

Formatting rules

  • Start with + and the country code
  • Drop the national trunk prefix, usually a leading 0
  • Remove spaces, dashes and brackets
  • Keep the total at 15 digits or fewer

How it applies to ZuteSIP

When you dial from the web dialer or a SIP app, and when you enter a ZuteSIP number into an app for verification, use the full international form. The country code tool and phone number formatter help convert local formats.

Related terms

  • DID
  • Mobile number
  • Caller ID

Frequently asked questions

Is the plus sign part of E.164?

The standard number is the digits; the plus is the conventional prefix that marks it as international and is widely expected by apps.

Why won't an app accept my number?

Check that you selected the right country and did not include the national leading 0.

How long can an E.164 number be?

Up to 15 digits, including the country code.

Does the US use a leading 1?

Yes, +1 is the country code for the US, Canada and other NANP countries.

Related pages

Get a number in these countries

Sources