E.164 is the ITU-T recommendation that defines international phone numbers. A number in E.164 form is a plus sign followed by a country code and the subscriber number, with no spaces or punctuation, and it is unambiguous anywhere in the world.
The rules.
| Standard | ITU-T Recommendation E.164 |
|---|---|
| Maximum length | 15 digits, excluding the leading + |
| Structure | + country code, then the national number |
| No national prefix | The trunk 0 used for domestic dialling is dropped |
| India example | +919876543210 |
| United Kingdom example | +442071838750, not +44 (0)20 7183 8750 |
Dropping the trunk zero is the step most often missed. A UK number written as +4402071838750 is not a valid E.164 number and will fail on some networks while working on others, which is the worst kind of bug to diagnose.
Where this shows up.
Every channel a contact page touches expects this format: tel: links, WhatsApp click-to-chat, vCard files, SMS gateways and CRMs. Storing one canonical E.164 number and formatting it for display is the arrangement that never breaks.
The common mistake.
Keeping the number in the shape it was typed. A page that stores 98765 43210 has a number that works only in one country and only when a human reads it — and that is discovered on the day somebody abroad tries to call.
Sources.
Every figure above is from one of these. They are the standard, the registry or the platform’s own documentation — read them rather than take our word for it.
- ITU-T Recommendation E.164: the international public telecommunication numbering plan International Telecommunication Union
- E.164 Wikipedia
- RFC 3966 — The tel URI for Telephone Numbers IETF