# E.164
> International telephone numbering standard that ensures globally unique phone numbers

E.164 is the ITU-T standard for international telephone number formatting used in VoIP systems.

## What is E.164?
E.164 is an international numbering standard defined by the ITU-T that specifies the format for telephone numbers worldwide. An E.164 number includes a country code, area code, and subscriber number, with a maximum of 15 digits (e.g., +1 212 555 1234).

## E.164 in VoIP
VoIP systems and [SIP](/voip-glossary/sip/) endpoints typically use E.164 formatted numbers for call routing. Consistent use of E.164 ensures interoperability between different carriers, PBX systems, and softphone clients across borders.

## Related Terms
- [SIP](/voip-glossary/sip/)
- [DID](/voip-glossary/did/)