Maximum Size for a phone number extension?

Question

Im trying to make a phone number extension field but Im not sure what the maximum amount of digits it can have and I dont see any sources online.

Answer 1

I was asking the same question myself but I couldn't find anything conclusive. I did, however, find a couple of useful bits of information that helped me come to a decision.

Robert Pepper at GetVoIP, says:

In an older PBX, that would be four digits, and limited to the same building. In a hosted PBX, it can be three, four or five digits, and the extension can be anywhere in the world, including your cell phone.

But, GoToConnect's website states:

An extension is a three to six-digit number identifying a specific call path configuration that allows you to dial and connect to another caller internally.

With that in mind, I decided to use six digits as a max length, until I learn otherwise.

Answer 2

Generally E.164 formatting using on apps.On this format max length is 15 this but using '+' for countrycode.

if you use Instead of '+' '00' it will be max 16 .