Phone numbers are written in dozens of local styles: (212) 555-0123, 020 7946 0123, 06 12 34 56 78. Computers need one consistent format, and that format is E.164, the international standard maintained by the ITU.
What E.164 looks like
An E.164 number is:
- a plus sign
- the country code (1 to 3 digits)
- the national significant number, with no trunk prefix, spaces or punctuation
- at most 15 digits in total, excluding the plus
| Local format | E.164 |
|---|---|
| 020 7946 0123 (UK) | +442079460123 |
| (212) 555-0123 (US) | +12125550123 |
| 089 1234567 (Germany) | +49891234567 |
| 06 1234 5678 (Italy) | +390612345678 |
| 22 123456 (Cyprus) | +35722123456 |
Notice the Italian example keeps its 0. We explain why in trunk prefixes and international dialling.
Why it matters
Routing. PBXs, SBCs and carriers match numbers exactly. If one system sends +442079460123 and another expects 02079460123, calls fail or land on the wrong extension.
Deduplication. A CRM that stores “020 7946 0123”, “+44 20 7946 0123” and “442079460123” as three different contacts is a data-quality problem. Store E.164 and format for display.
Messaging and APIs. SMS and voice APIs almost universally expect E.164 input.
Microsoft Teams. Numbers assigned to Teams users must be in E.164. See connecting DIDs to Teams.
Converting to E.164
- Identify the country.
- Remove spaces, brackets and dashes.
- Remove the domestic trunk prefix if the country uses one (usually 0, or 1 in North America).
- Add + and the country code.
Don’t write your own rules for every country. Use a maintained library such as Google’s libphonenumber, which knows each country’s lengths, prefixes and exceptions.
Display vs storage
Store E.164. Display in the format your audience expects: national format for domestic customers, international format (+44 20 7946 0123) for everyone else.
Frequently asked questions
Is E.164 the same as the “+” format on my phone?
Almost. Phones show spaces for readability; E.164 is the same digits without spaces.
Do short codes fit E.164?
No. Short codes and emergency numbers are national-only and not part of E.164.
Explore numbering facts for every country