E.164 Format: How to Write a Phone Number the International Way

A signup form, a CRM import or an ads account asks for a phone number "in E.164 format." Short answer: a plus sign, the country code, then the rest of the number with nothing in between. A US number written 201-555-0123 goes in as +12015550123.

Google Ads' help page puts it plainly: the format should contain only digits, with no spaces, hyphens, parentheses or other separators. The rest of this guide explains where that rule comes from, and why the same number printed on a business card legitimately looks different.

What E.164 actually is

E.164 is the ITU-T Recommendation behind the international public telecommunication numbering plan. For an ordinary phone number it defines two parts: a country code and a national (significant) number, which the standard abbreviates N(S)N.

What it doesn't do is tell you where to put spaces. E.164 hands the use and printing of symbols and separators to a sister standard, ITU-T E.123. Keep that split in mind. It explains why guides seem to disagree about spaces.

The E.164 rules you need to know

• The country code comes first and has from one to three digits. It identifies the destination country.
• An international number for a geographic area can have no more than 15 digits, counting the country code and national number together.
• The international prefix used to place a call from your location does not count toward that 15-digit limit.
• With a one-digit country code such as +1, the national number can contain up to 14 digits.
• Leave out the national (trunk) prefix, like the 0 in the E.123 example further down. It isn't part of the national number and must not be dialed on international calls.

The plus sign is not an extra digit in the phone number. E.164 recommends it as an indicator that an international prefix is required, while E.123 places it before the country code.

So the + is a placeholder. You swap it for the international prefix of the country you're calling from, and that prefix differs from country to country. For countries defining or revising their numbering plans, the ITU recommends 00 as that prefix.

E.164 format versus E.123 display format

Because E.164 leaves printing to E.123, one number can legitimately appear in three shapes depending on who, or what, reads it:

For printed international numbers, E.123 says to use spaces only as separators. It calls for a space after the country code and another between the trunk or area code and subscriber number.

So spaces can be appropriate when you are showing a number to a person. They are not appropriate in a field that specifically demands the compact digits-only version after the plus sign.

Clickable tel: links follow a third set of rules. RFC 3966 says globally unique telephone numbers should begin with + and be built from the country code and national number under E.123 and E.164. Its example, tel:+1-201-555-0123, uses hyphens only to make the country code, area code, and subscriber number easier to read. Those visual separators do not affect number comparison or call placement.

How to write a US number in E.164 format

Start with +1, then add the full 10-digit North American number. NANP numbers consist of a three-digit area code followed by a seven-digit local number.

Take the RFC 3966 example number, 201-555-0123. Drop the hyphens and put +1 in front: +12015550123. On a printed page, the E.123 version is +1 201 555 0123, with a space after the country code and another after the area code.

Don't type your own exit code into the field. The + already signals that step.

The North American Numbering Plan is shared by 20 North American countries, not just the United States. The ITU assigned country code 1 to the entire NANP area, which conforms with E.164.

That means a country code 1 number is not automatically a US number. Our US phone number format page covers how numbers are written domestically.

How to convert a foreign number with a leading 0

The trunk prefix gets a clear rule in E.164: the national (trunk) prefix is not part of the national number, and it must not be dialed at the international level.

E.123 gives a clear example: a number displayed nationally as (0609) 123 4567 becomes +22 609 123 4567 internationally. The leading 0 and the parentheses disappear.

To do it yourself: write + and the country code, drop the trunk prefix, keep every remaining digit, then strip the spaces if the field wants the compact form.

The catch is knowing which digit is the trunk prefix in a given country. Don't strip a zero just because it comes first. Check the country's own format before you edit, for example our UK phone number format and German phone number format pages.

Common E.164 entry mistakes

• Keeping the trunk prefix. The international form never includes it.
• Putting an international access prefix into the stored number. The access prefix is outside the E.164 number and does not count toward its maximum length.
• Using dashes or parentheses in a strict platform field. Google Ads, for one, wants digits only.
• Assuming +1 means the United States. Country code 1 serves the whole NANP area.
• Counting the plus sign as a digit. The number is made of decimal digits, up to 15 of them; the + is a symbol, not one of them.

Storing a number and dialing it are different jobs. When you actually place the call, you replace the + with your own exit code; the international calling guide lists them.

FAQ

What is E.164 format?

It's the ITU international numbering recommendation in which a geographic-area number is made up of a country code followed by a national (significant) number. On platforms such as Google Ads, "E.164 format" means the compact entry style: + and digits, no separators.

How many digits can an E.164 number have?

An international E.164 number for a geographic area can have a maximum of 15 digits. The international access prefix used from your calling location is excluded from that total.

How do I write a US number in E.164 format?

Use +1 followed by the 10-digit NANP number. NANP numbers have a three-digit area code and a seven-digit local number. For example, the RFC 3966 US example can be entered in compact form as +12015550123.

Do I keep the leading 0 when converting a foreign number?

No, not when the leading 0 is the national trunk prefix. E.164 excludes that prefix from the national number for international calling. E.123’s example changes (0609) 123 4567 to +22 609 123 4567.

Does E.164 allow spaces or dashes?

Not on its own terms. It leaves printed symbols and separators to E.123. E.123 uses spaces for printed international numbers, while a strict platform field may require digits only after the + sign.

Is +1 always a US number?

No. The ITU assigned country code 1 to the full North American Numbering Plan area, which is shared by 20 North American countries.

Sources

1. Google Ads Help: E.164 format: Definition (accessed 2026-09-24)
2. IETF / RFC Editor: RFC 3966: The tel URI for Telephone Numbers (accessed 2026-09-24)
3. International Telecommunication Union: Recommendation ITU-T E.164 (02/2026): The international public telecommunication numbering plan (accessed 2026-09-24)
4. International Telecommunication Union: Recommendation ITU-T E.123 (02/2001): Notation for national and international telephone numbers, e-mail addresses and web addresses (accessed 2026-09-24)
5. North American Numbering Plan Administrator: About NANPA (accessed 2026-09-24)