A Fully Qualified Domain Name - How Many Characters?

A full domain name can have maximum of 253 characters. 

Each label within a domain name - the parts of the domain name between dots - is limited to 63 characters.

Domains are limited to numbers (0-9), letters (a-z), and hyphens (“-“). Valid names cannot begin or end with a hyphen, and can't have a hyphen in both the 3rd and 4th position. E.g., do--main.com is not allowed, but d--omain.com is fine.

Internationalized Domain names, IDNs, enable people around the world to use domain names in local languages and scripts. IDNs are formed using characters from different scripts, such as Arabic, Chinese, Cyrillic or Devanagari. Not all domain extensions support IDNs.

Spaces are not permitted. 

Note: Domain names are not case sensitive (i.e. DomainName.com is the same as domainname.com).