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Texting and SMS

SMS international format: how to write a number so the text arrives

Reviewed by Sujan ThapaliyaLast updated

The short answer

International standard format is E.164: a plus sign, the country code, then the national number with no spaces, dashes or leading trunk zero. A UK mobile written 07700 900123 becomes +447700900123. That single form works from every country and every platform.

When a form rejects your number and asks for international standard format, it is asking for one specific thing, and the error message almost never says what.

What does the format actually look like?

Plus sign, country code, national number. No trunk zero, no spaces, no dashes.
CountryWritten locallyInternational standard format
United Kingdom07700 900123+447700900123
United States(415) 555-0123+14155550123
Germany030 901820+4930901820
India098765 43210+919876543210
Australia0412 345 678+61412345678

The maximum length is fifteen digits including the country code, set by the ITU recommendation the format comes from. Anything longer is not a valid number, whatever the form accepted.

Why does the leading zero have to go?

It is not part of the number. The zero is a trunk prefix — a dialling instruction meaning this is a national call — and it exists only for calls placed inside that country. The country code takes its place, so keeping both produces a number wrong by one digit in a way that looks entirely plausible.

This is the most common cause of failed international messages, and it fails quietly: platforms often accept the number, attempt delivery and report nothing useful. The mechanics are in trunk prefix and E.164.

How do you convert a number reliably?

  1. 1

    Find the country code

    The dialling code for the destination — 44 for the UK, 1 for the US and Canada, 91 for India. The country calling code directory lists every one.
  2. 2

    Strip the trunk prefix

    Remove the leading 0 domestic writing uses. A few countries do not use one, and a small number keep a digit that looks like one, which is why converting by hand goes wrong at scale.
  3. 3

    Remove all punctuation

    No spaces, dashes, brackets or dots. Formatting is for display; storage should be digits and a plus.
  4. 4

    Check the length

    Fifteen digits maximum including the country code. A longer result means something was kept that should have gone.

Convert once, at input

Normalising numbers as they enter your system rather than as you send removes a whole class of duplicate-contact bugs — the same person stored three ways is three records and three separate messages. The phone number formatter does it in the browser, free, with nothing submitted.

What else changes when texting across borders?

  • Rates differ sharply by destination, far more than domestic messaging does. Model the destinations you actually send to rather than an average.
  • Delivery is less consistent. More networks are involved, and some destinations require the sender to be pre-registered before traffic delivers at all.
  • Sender identity behaves differently. Some countries display an alphanumeric sender name, others force a numeric one, and a few overwrite whatever you send.
  • Local rules apply, not yours. Consent, timing and content rules follow the recipient's jurisdiction, and several are stricter than the rules at home.

Frequently asked questions

What is the international standard format for an SMS number?
E.164: a plus sign, the country code, then the national number with the trunk prefix removed and no spaces or punctuation. +447700900123, not 07700 900123 and not 00447700900123.
Do I remove the leading zero?
Yes, in almost every country that uses one. The zero is a domestic dialling instruction and the country code replaces it. 020 7946 0958 in the UK becomes +44 20 7946 0958 — never +44 020.
Can I use 00 instead of the plus?
Only from countries where 00 is the exit code. The plus is the portable form: handsets and platforms translate it to whatever the local exit code is, which is why contact databases should store it that way.
How do I text a number in another country?
Save it in E.164 and send normally. If it fails, the number is nearly always the problem rather than the network — a leading zero left in, a missing country code, or punctuation a platform rejected.
Does international texting cost more?
Yes, and rates vary widely by destination. Delivery is also less consistent, because the message crosses more networks — which is why bulk international sending needs per-destination testing rather than one assumption.

Sources

  1. ITU-T Recommendation E.164 — The international public telecommunication numbering plan — International Telecommunication UnionThe international number format, the 15-digit maximum, and how country codes and national numbers compose.
  2. Messaging Principles and Best Practices — CTIACarrier expectations for A2P messaging: 10DLC registration, opt-in and opt-out handling, and content rules.

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