E.164 format is the ITU standard for international phone numbers: a country code of 1 to 3 digits followed by the national number, at most 15 digits in total, with no international prefix, spaces or national trunk zero. Wholesale carriers route and bill on E.164 numbers, so normalizing your dial plan to E.164 before sending calls avoids most routing errors and billing surprises.
How an E.164 number is built
| Part | Example (UK mobile) | Notes |
|---|---|---|
| Country code | 44 | 1 to 3 digits, assigned by the ITU |
| National number | 7700900123 | Without the domestic trunk prefix (the leading 0) |
| Full E.164 | 447700900123 | Often written +447700900123; maximum 15 digits |
The plus sign shows that the number is in international format. Some carriers want it in the SIP request and some do not; agree this during interconnect setup.
Common normalization rules
- Remove international prefixes: 00 (used in most countries) and 011 (used in North America) must not be sent as part of the number.
- Remove the national trunk prefix: a UK number dialed as 07700 900123 becomes 44 7700 900123.
- Watch the exceptions: in Italy, fixed numbers keep their leading 0 after the country code (39 06 ...), because the 0 is part of the number, not a trunk prefix.
- North America: country code 1 is shared by the US, Canada and many Caribbean countries. The 3 digit area code decides the destination and the rate, so 1 alone is never enough to route.
- Strip formatting: spaces, dashes, brackets and dots.
Why it matters for routing and billing
Carriers match the dialed number against their rate deck by longest prefix. A number sent with an extra 0, or without the country code, either fails or matches the wrong prefix, sometimes a more expensive one. The breakout a call falls into depends on getting the first digits right.
Caller ID format
The calling number (CLI) should also be sent in E.164. Many destination networks reject or strip a caller ID that is not a valid, complete number, and in the US an invalid CLI can affect STIR/SHAKEN handling and call labeling. If you see calls arriving without your number, check its format first. See how to check CLI delivery.
Tech prefixes and dial plans
Many carriers use a tech prefix: a few digits added before the E.164 number to identify the customer account or the route quality, for example 1234#447700900123. The prefix is removed by the seller's switch before the call goes on. Keep the tech prefix separate from the number in your configuration so your own CDRs still show clean E.164 numbers, which you need for billing checks and CDR reconciliation.
Validating numbers before dialing
Number length and valid ranges differ by country. Validating lists against the national numbering plan before a campaign reduces failed attempts and keeps ASR up. For mobile numbers, a lookup can also show whether the number was ported to another operator. See number portability and routing.
Send clean numbers, get clean routes
VoIPMatcher works with E.164 numbers on every VoIP termination route it sources. Request a voice route for your destinations.
Frequently asked questions
What is an example of an E.164 phone number?
A UK mobile number dialed nationally as 07700 900123 becomes +447700900123 in E.164: country code 44, then the national number without the leading 0. An Australian mobile dialed as 0412 345 678 becomes +61412345678. There are no spaces, dashes, brackets or international prefixes such as 00 or 011.
How do I format a US number in E.164?
Put country code 1 in front of the 10 digit number made of the 3 digit area code and the 7 digit local number, and remove spaces, brackets and dashes. For example, (212) 555-0100 becomes +12125550100, or 12125550100 if your carrier wants digits only. Never send the 011 international prefix.
Does E.164 format include the plus sign?
The plus sign is the usual written form and shows that the number is international, but it is not counted among the 15 digits. Some carriers and APIs expect it in SIP messages or requests, others want digits only. Agree the exact format with each carrier during interconnect setup and keep it consistent.
What is a regex for E.164 format?
A common validation pattern is ^\+?[1-9]\d{1,14}$: an optional plus sign, a first digit that is not zero, and at most 15 digits in total. It only checks the shape of the number. Real validation needs each country's numbering plan, because valid lengths and number ranges differ from country to country.
Is E.164 the same as international format?
Nearly. E.164 is the ITU standard behind the international format: country code plus national number, up to 15 digits. The written international format often adds spaces for readability, such as +44 7700 900123, while E.164 as used by systems and carriers is the same digits with no spaces or punctuation.
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