The international phone number format is a plus sign followed by a country code and the national number, written as digits, with up to 15 digits after the plus sign. A UK number written 020 7946 0958 inside the country therefore becomes +44 20 7946 0958 abroad, because the country code is added and the domestic trunk zero is removed.
Those two changes decide whether a call connects, whether a text message is delivered, and whether a customer relationship management (CRM) system recognises two records as one contact. Errors in them tend to show up late, usually when a campaign reports low connect rates, because a malformed number can fail silently inside the CRM.
The sections below cover the standard, country and area codes, the leading zero, CRM storage, validation and a clean-up sequence for large databases. Each rule was checked against ITU-T Recommendation E.164, the documentation of libphonenumber (an open-source phone number library maintained by Google), HubSpot’s phone validation rules and Twilio’s guidance.
What is the international phone number format?
It is the layout set by E.164, the numbering standard of the Telecommunication Standardisation Sector of the International Telecommunication Union (ITU-T). The plus sign is notation that signals a country code follows, and a phone replaces it with the local exit code when dialling, for example, 011 in the United States, 00 in the United Kingdom, and 0011 in Australia.
The 15-digit limit covers the complete number. It counts the country code and leaves out the plus sign, any exit code such as 011 or 00, and any extension, so the length of the country code only changes how many digits remain for the rest of the number, which is 14 after a one-digit code and 12 after a three-digit code.
A field sized for 16 characters, the plus sign and 15 digits, holds every valid E.164 value. A stored value contains only the plus sign and digits, so it reads the same in every system.
How do country codes and area codes fit into the international phone number format?
A country code identifies the country or numbering plan, runs from one to three digits and always begins with a digit from 1 to 9. The codes met most often in B2B data are these:
- +1 for the United States, Canada and Caribbean members of the North American Numbering Plan (NANP)
- +44 for the United Kingdom, +49 for Germany, +91 for India, +61 for Australia
- +353 for Ireland and +971 for the United Arab Emirates, both with three digits
- +7 for Russia and Kazakhstan, where the digits after the code decide the country
- +52 for Mexico, which belongs to a separate numbering plan from the NANP
Area codes, which the ITU calls national destination codes, stay in the number between the country code and the subscriber number. Their length varies: NANP numbers carry a three-digit area code and a seven-digit subscriber number, Mexican numbers carry 10 digits after +52 whatever the area code length, Singapore uses a single national plan of eight-digit numbers, and Australian mobiles begin with the 04 prefix in place of an area code.
A +1 prefix proves membership of the North American plan only, since the area code that follows can point to Toronto or Bermuda as easily as to New York.
Also Read: A Beginner’s Guide to Conversion Optimisation in B2B Marketing
Should the leading zero be dropped in the international phone number format?
Usually yes. Many countries add a trunk prefix, most often a zero, for calls placed inside the country, and it serves domestic dialling only, so keeping it produces +44 020 or +61 04, both of which are incorrect and can fail to connect. Italy is a well-known exception that breaks automated cleaning rules: Italian landlines keep the zero after +39, and the libphonenumber documentation names Italy as a case where the zero is needed for dialing from abroad and is therefore stored as part of the national number. San Marino (+378) numbers keep their leading 0549 in the same way, and Vatican City numbers use Rome’s +39 06 range, so both follow the Italian rule.
Three rules remove the zero correctly:
- Parse with a maintained library and pass the record’s country as the default region. A number written without a plus sign needs a known region before it can be interpreted.
- Treat ’00’ and ‘+’ as different things. The United States uses 011, libphonenumber documents that the international prefix differs by country, and Twilio’s own E.164 pattern rejects the 00 form that is often used in Germany.
- Retire old Mexican formats. Mexico moved to a flat 10-digit plan on 3 August 2019, abolished the 01, 044 and 045 prefixes, and dropped the extra 1 after +52 for mobiles, with the older +521 form tolerated until August 2020.
How should international phone numbers be stored in a CRM?
One E.164 value, written in the international phone number format, goes in the database, and the screen shows it in whatever local style a representative expects. HubSpot’s phone validation follows this logic: it requires a valid country code beginning with a plus sign, matches the number against the pattern of that country, saves the value without formatting and displays it in a regional style. Its documentation also shows why the area code check matters, because +1 (123) 456-7890 fails validation as 123 falls outside the valid US area codes.
These four storage mistakes break matching and delivery:
- Numbers pasted into a spreadsheet number cell, which can strip the plus sign and any leading zero
- Spaces, dashes or brackets saved inside the value, so identical numbers fail an exact match
- Imports without a country code, which force one default country onto every row or leave the number unparsed
- Extensions typed into the number field, when E.164 covers only the dialable number
Different spellings of one number are a common source of duplicate contacts. Once every number shares one format, the duplicates are easy to find, and CRM cleaning for duplicate contacts can merge them.
Also Read: Data Quality Checks to Test Your Business Data Today
How is an international phone number validated?
Validation of the international phone number format has four layers, and a number that passes one layer can still fail the next.
The libphonenumber library separates the second and third layers on purpose, with a possible-number check that examines length only and a valid-number check that applies the full rules of the country. It also reports line type, which often needs a lookup because US, Canadian and Mexican mobiles and landlines follow the same pattern. The last layer needs data beyond the format rules. Confirming that a line responds is the job of B2B data verification services.
The first layer is usually a regular expression, the same one Twilio publishes for E.164 values:
^\+[1-9]\d{1,14}$
The first digit after the plus sign must be 1 to 9, because every country code begins with a digit from 1 to 9, and \d{1,14} allows one to 14 further digits, so the value after the plus sign runs from 2 to 15 digits, which matches the E.164 ceiling. The lower end is a loose bound, since E.164 leaves the minimum length open, and the shortest complete numbers in use, such as those of Saint Helena (+290) and Niue (+683), run to about 7 digits, so a value of 2 to 6 digits matches the pattern while falling short of the shortest numbers in use. The possible-number check by country is what rejects values too short for the country. The pattern checks shape and length only, so a value that begins with an unassigned country code passes it. Twilio itself notes that the pattern also matches invalid numbers and recommends a lookup service for full validation.
How to fix international phone number format errors in a large B2B database
These steps run in this order because the parser needs the country before it can read any number:
- Audit the country field. The parser needs a default region for every record, so missing or wrong countries come first.
- Convert every number to E.164 with a parser. Failures go to a review file for manual handling.
- Remove duplicates after standardising. Two spellings of one number only match once they share a format.
- Run the possible and valid checks, then separate mobiles from landlines.
- Fill the empty fields and verify a sample by call or lookup. A parser cannot supply a missing number, so phone number appending is the route for empty fields, and its service page describes international numbers delivered with standardised country codes and formats.
Which international phone number format should be used in 2026?
E.164 is the right storage format for databases that feed diallers, SMS platforms and CRM validation rules. A database that follows E.164 needs four things:
- One phone field holding the E.164 value
- A separate country field that feeds the parser
- A display layer showing national style to local representatives and international style to mixed audiences
- Validation at entry and again after every import, merge or migration
Data appending and enrichment should wait until every record follows that international phone number format, because new numbers loaded into inconsistent fields add duplicates without adding reachable contacts.
A display format can always be produced from an E.164 value, but an E.164 value can be rebuilt from a display format only when the country is known, since any number written without a plus sign is read against a default region. A wrong or empty country field therefore breaks the parse before any format rule applies, which makes it the likely source of many formatting failures in B2B databases, while the phone column only reveals the result. Teams that plan market by market can build each batch from country-wise B2B data, so the country is known before any number is parsed.
What should be checked first in an existing database?
A free CRM data health check gives a view of duplicates and inconsistencies across the whole CRM, and a 200-record audit then narrows the focus to phone numbers. The audit shows whether the country field or the phone field needs work first, and it applies the international phone number format to a sample before any large clean-up begins:
- Export 200 random records.
- Parse each number with libphonenumber, using the record’s own country.
- Sort the results into these four groups:
- Parsed cleanly
- Parsed only after a trunk zero or an old prefix was corrected
- Ambiguous, because the country is missing or contradicts the prefix
- Invalid
A large ambiguous group means the country field needs repair before any format rule is applied to the full database. If corrected and invalid numbers dominate instead, the stored values need the conversion described above, followed by a second sample to confirm that the error rate has fallen.
Also Read: Data Enrichment vs Data Cleansing: Which Does Your CRM Need?
What should happen to records that fail the checks?
After the conversion and the second sample, records still left in the invalid or ambiguous groups usually need outside data rather than another parser run, because a parser works only with the digits already stored and can confirm neither a missing number nor a responding line. Appending missing numbers fills the empty fields, and verifying stored ones confirms that a line responds.
A practical order is to run up to 100 of those records through both steps, compare the returned numbers with the stored ones, and commit the full batch once the match rate looks right. A second CRM data health check after the load then shows whether the new numbers introduced duplicates or inconsistencies, which keeps the database ready for diallers and SMS platforms.
FAQs
How is the difference between a country code and an area code defined?
A country code identifies the country or numbering plan and comes first, while an area code identifies a region inside it and comes second. Both exist inside a +1 number, which is why +1 alone leaves open whether a contact is in the United States, Canada, or the Caribbean.
How is an international number dialled from the United States?
The caller dials 011, then the country code, then the national number without its trunk prefix, so 020 7946 0958 in the UK is dialed as 011 44 20 7946 0958. Mobile phones usually accept a plus sign in place of 011 and substitute the correct exit code automatically.
How should an extension be stored?
E.164 covers only the dialable number, so an extension belongs in its own field. HubSpot accepts a pattern such as +18779290687 ext123 on import, which keeps the main number intact.
How should a clickable phone link be written?
The link should carry the complete E.164 value, for example, tel:+442079460958. RFC 3966 treats a number that starts with a plus sign as a global number that works from any country, while a number without it counts as local and needs a context parameter, and the standard also defines an extension parameter for the same link.
What country code should a record receive when no country is stored?
The record’s other data decides it, such as the company headquarters country, the address on the lead, or the country chosen in a form. A blanket +1 default produces a wrong country code for every record from another country, so ambiguous rows belong in a review queue for manual checking.
Why does an SMS platform reject a number that looks correct?
Platforms such as Twilio require E.164 for messaging, so a value with brackets, a trunk zero or a missing country code can look correct to a person and still fail the parser. Reformatting the field to E.164 normally resolves the rejection.
Can letters appear in an international phone number?
E.164 allows digits only, so a vanity number written with letters is converted to digits using the standard keypad mapping before storage. The converted digits are the value that should be validated and saved.