# What is E.164?

> E.164 is the ITU-T international public telecommunication numbering plan — the worldwide standard format for phone numbers. An E.164 number is a country code followed by a national subscriber number, up to 15 digits total, written with a leading '+' (for example +9714XXXXXXX). Every MSISDN follows E.164. Passing numbers in strict E.164 form is the single most reliable way to avoid routing and delivery failures on an A2P SMS API.

- Canonical URL: https://www.broadnet.me/answers/what-is-e164
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Anatomy of an E.164 number

A '+' prefix, then a 1-3 digit country code, then the national subscriber number — 15 digits maximum in total, with no spaces, dashes, or national trunk prefixes. The '+' tells every network the digits that follow are internationally routable, removing the ambiguity of local dialling conventions. See /answers/what-is-msisdn.

## Why E.164 prevents delivery bugs

The commonest cause of failed A2P sends is a number in a local format — a leading 00, or a national 0 that should have been stripped. Normalising every number to E.164 before submission, and validating it with HLR Lookup (which also reveals the current, possibly ported, operator), removes an entire class of delivery failures. See /products/hlr-lookup.

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [What is an MSISDN?](https://www.broadnet.me/answers/what-is-msisdn)
- [What is ENUM (E.164 Number Mapping)?](https://www.broadnet.me/answers/what-is-enum)
- [What is MNP (Mobile Number Portability)?](https://www.broadnet.me/answers/what-is-mnp)
- [What is HLR Lookup?](https://www.broadnet.me/answers/what-is-hlr-lookup)
- [SMS API](https://www.broadnet.me/products/sms-api)
- [HLR Lookup](https://www.broadnet.me/products/hlr-lookup)