E.164 vs E.123 Phone Number Formats: What's the Difference?
Understand the difference between E.164 and E.123 phone number formats, when to use each, and how to convert between them for SMS APIs, databases, and display.
Two ITU-T standards dominate phone number formatting: E.164 (for machines) and E.123 (for humans). Using the wrong one causes failed API calls, broken validations, and confused users.
Here’s the practical difference and when to use each.
Quick Comparison
| E.164 | E.123 | |
|---|---|---|
| Purpose | Storage & transmission | Display & print |
| Example | +14155552671 | +1 415 555 2671 |
| Spaces | None | Yes (between groups) |
| Max length | 15 digits + + | No strict limit |
| Used by | SMS APIs, databases, telecom systems | Business cards, websites, documents |
| ITU-T Standard | ITU-T E.164 | ITU-T E.123 |
E.164 Format
E.164 is the machine-readable international phone number format defined by the International Telecommunication Union (ITU-T).
Rules
- Starts with
+ - Followed by country code (1–3 digits, first digit non-zero)
- Followed by subscriber number
- Total digits: 7–15 (not counting the
+) - No spaces, dashes, parentheses, or other formatting
Examples
| Country | E.164 Format | Breakdown |
|---|---|---|
| US | +14155552671 | +1 (country) + 4155552671 (number) |
| UK | +442071234567 | +44 (country) + 2071234567 (number) |
| India | +919876543210 | +91 (country) + 9876543210 (number) |
| Germany | +4930123456 | +49 (country) + 30123456 (number) |
| Japan | +81312345678 | +81 (country) + 312345678 (number) |
| Australia | +61412345678 | +61 (country) + 412345678 (number) |
When to Use E.164
- Database storage — always store numbers in E.164
- SMS APIs — Twilio, Vonage, MessageBird all require E.164
- CRM systems — Salesforce, HubSpot normalize to E.164
- Comparisons and deduplication — one canonical format eliminates mismatches
- Programmatic processing — no ambiguity for code to parse
E.123 Format
E.123 is the human-readable format designed for print and display. It adds spaces between logical groups to make numbers easy to read.
Rules
- International format starts with
+and country code - Groups separated by spaces
- National format can omit the country code
- Grouping varies by country’s numbering plan
- No strict maximum length
Examples
| Country | E.123 International | E.123 National |
|---|---|---|
| US | +1 415 555 2671 | (415) 555-2671 |
| UK | +44 20 7123 4567 | 020 7123 4567 |
| India | +91 98 7654 3210 | 098 7654 3210 |
| Germany | +49 30 123456 | 030 123456 |
| Japan | +81 3 1234 5678 | 03-1234-5678 |
When to Use E.123
- User-facing display — show formatted numbers on websites
- Business cards and print — readability matters
- Input fields — let users type in their local format
- Documentation — written guides and manuals
Converting Between Formats
E.123 → E.164 (strip formatting)
function toE164(phone) {
return phone.replace(/[\s\-\(\)\.]/g, '');
}
toE164('+1 (415) 555-2671'); // '+14155552671'
toE164('+44 20 7123 4567'); // '+442071234567'E.164 → E.123 (add formatting)
This requires knowing the country’s numbering plan. Here’s a simplified approach for common countries:
function toE123(e164) {
// US/Canada (+1)
if (e164.startsWith('+1') && e164.length === 12) {
const area = e164.slice(2, 5);
const mid = e164.slice(5, 8);
const last = e164.slice(8);
return `+1 ${area} ${mid} ${last}`;
}
// UK (+44)
if (e164.startsWith('+44') && e164.length === 13) {
const area = e164.slice(3, 5);
const part1 = e164.slice(5, 9);
const part2 = e164.slice(9);
return `+44 ${area} ${part1} ${part2}`;
}
// India (+91)
if (e164.startsWith('+91') && e164.length === 13) {
const part1 = e164.slice(3, 5);
const part2 = e164.slice(5, 9);
const part3 = e164.slice(9);
return `+91 ${part1} ${part2} ${part3}`;
}
// Generic fallback: insert space after country code
return e164.replace(/^(\+\d{1,3})(\d+)$/, '$1 $2');
}Python
import re
def to_e164(phone: str) -> str:
return re.sub(r'[\s\-\(\)\.]', '', phone)
def to_e123_us(e164: str) -> str:
"""Convert US E.164 to E.123"""
if e164.startswith('+1') and len(e164) == 12:
return f"+1 {e164[2:5]} {e164[5:8]} {e164[8:]}"
return e164Google Sheets
E.123 → E.164:
=REGEXREPLACE(A2, "[\s\-\(\)\.]", "")E.164 → E.123 (US):
=IF(LEFT(A2,2)="+1",
"+1 " & MID(A2,3,3) & " " & MID(A2,6,3) & " " & MID(A2,9,4),
A2)The Practical Rule
Store as E.164. Display as E.123.
User types: (415) 555-2671 ← E.123 (human input)
↓
You store: +14155552671 ← E.164 (database)
↓
You display: +1 415 555 2671 ← E.123 (UI)
↓
API sends: +14155552671 ← E.164 (Twilio/Vonage)This pattern works for every country and every use case. The user never sees or cares about E.164 — but your systems always use it internally.
Validation Regex
E.164
^\+[1-9]\d{6,14}$E.123 (loose — allows spaces)
^\+[1-9][\d\s]{6,20}$Common Mistakes
1. Storing E.123 in Your Database
// Bad — inconsistent formats cause deduplication failures
"+1 415 555 2671"
"(415) 555-2671"
"14155552671"
// Good — one canonical format
"+14155552671"2. Sending E.123 to SMS APIs
Twilio, Vonage, and MessageBird all require E.164. Sending +1 415 555 2671 (with spaces) will fail or behave unpredictably.
3. Displaying E.164 to Users
+14155552671 is hard to read. Always format for display using the national convention users expect.
4. Assuming All Numbers Are 10 Digits
Country codes range from 1–3 digits, and subscriber numbers vary from 4–12 digits. Don’t hardcode length assumptions.
Related Resources
- E.164 Phone Number Validator — validate numbers online
- Phone Number Formatter — convert to E.164
- Phone Number Regex Patterns — copy-paste regex for validation