# E.164 phone number format

> E.164 is the international phone number format: a plus sign, a country code and up to 15 digits in total. Why APIs use it and how to convert to it.

Canonical: https://mobilevalidate.com/glossary/e164 · Last updated: 2026-09-25

![A cell tower sends signal to a SIM card; the line type is identified as mobile rather than landline or VoIP.](https://mobilevalidate.com/images/carrier-and-line-type-lookup.svg)

*Carrier lookup returns the line type (mobile, landline or VoIP) and the network behind the number.*


E.164 is the international standard format for telephone numbers: a plus sign, the country code, then the national number, with no spaces or punctuation, and at most 15 digits in total. `+447700900001` is a UK mobile number written in E.164. The format is defined in ITU-T Recommendation E.164, published by the International Telecommunication Union.

## What does an E.164 number consist of?

It has three parts:

| Part | Example (`+447700900001`) | Notes |
|---|---|---|
| `+` | `+` | Stands for the international dialling prefix (00, 011, etc.) |
| Country code | `44` | 1 to 3 digits, assigned by the ITU |
| National significant number | `7700900001` | The number without the national trunk prefix (the leading 0 in the UK) |

The maximum length is 15 digits, excluding the `+`. Country codes can be shared. `+1` covers the United States, Canada and a number of Caribbean countries (the North American Numbering Plan), and `+7` covers Russia and Kazakhstan. The country code alone doesn't always identify the country. The first digits of the national number are needed too.

## Why do APIs use E.164?

A number can be written in dozens of ways: `07700 900001`, `+44 (0)7700 900001`, `0044 7700-900001`. They all mean the same line. Converting everything to one canonical form is the only reliable way to:

- **deduplicate** a list, so the same person isn't checked or messaged twice;
- **cache** results per number;
- **price and route** per country;
- **match** numbers across systems (CRM, messaging provider, fraud tools).

MobileValidate converts every number to E.164 before deduplication, caching, pricing or any check. The `e164` field in each result shows the converted form, and `number_status` shows whether the input was valid, invalid or a duplicate.

## How do you convert a national number to E.164?

1. Remove spaces, dashes, dots and brackets.
2. Remove the national trunk prefix (usually a leading `0`; in North America a leading `1` dialled domestically).
3. Add `+` and the country code.

So `07700 900001` in the UK becomes `+447700900001`, and `(202) 555-0143` in the US becomes `+12025550143`. Because step 3 needs the country, national-format input needs a country hint. In the API that is the `default_country` field (ISO code, for example `"GB"`). Well-maintained libraries such as Google's libphonenumber also check length and number ranges per country, which catches many typos before any check is paid for.

## Is a valid E.164 number a working number?

No. E.164 describes the *format* and whether the number fits the country's numbering plan. It says nothing about whether the number is assigned, reachable or in use on a messaging app. The [number reachability](/glossary/number-reachability) entry explains the difference. To learn more, use a [carrier lookup](/services/carrier-lookup) for line type and network, and channel checks such as the [WhatsApp check](/services/whatsapp-number-check).

## Which numbers are safe to use in examples?

Use ranges reserved for fiction. In the UK, Ofcom reserves `07700 900000` to `07700 900999` for drama and they are never assigned to subscribers. MobileValidate's [test mode](/docs/test-mode) uses numbers from this range, such as `+447700900001`.

## Frequently asked questions

### How long can an E.164 number be?

At most 15 digits, counting the country code but not the plus sign. The ITU-T E.164 recommendation sets that limit.

### Do I have to send numbers in E.164 to the MobileValidate API?

No. The API accepts common formats and converts them. National formats such as 07700 900001 need default_country (for example GB) so the country code can be added. Results always include the e164 form.

### Should I keep the leading zero of a national number?

No. The national trunk prefix (0 in most of Europe, 1 in North America when dialled domestically) is dropped in E.164. 07700 900001 in the UK becomes +447700900001.