What is the Maximum Length of a Domain Name?

Published July 10, 2024

Problem: Domain Name Length Limits

When creating a website, choosing the right domain name matters. Many people ask about the maximum length for a domain name. This question comes up because domain names have technical limits and practices that affect how easy they are to use and remember.

Maximum Length for Domain Name Components

Label Length (Subdomain)

The maximum length for individual labels (subdomains) in a domain name is 63 octets. This limit applies to each part of the domain name separated by dots. For example, in "www.example.com", "www", "example", and "com" are all separate labels, and each can be up to 63 octets long.

It's better to keep labels shorter than the maximum limit. Shorter labels are easier to type, remember, and less prone to errors. Most website owners use labels that are much shorter than the 63-octet limit for better usability.

Tip: Optimal Label Length

Aim for label lengths between 3 to 15 characters. This range balances memorability with flexibility, allowing for descriptive yet concise domain names.

Full Domain Name Length

The total character limit for entire domain names, including all labels and dots, is 253 octets. This limit applies to the complete domain name as a whole. For instance, "www.example.com" counts as one full domain name.

There are technical reasons for this full name length restriction. The 253-octet limit allows for compatibility with various internet protocols and systems. It helps maintain consistency across different applications and services that handle domain names. This limit also helps prevent issues with data storage and transmission in DNS servers and other network infrastructure.

Technical Standards and Specifications

RFC 1035 Guidelines

RFC 1035, published in November 1987, set the foundation for domain name specifications. This document outlines the structure and limits for domain names in the Domain Name System (DNS).

RFC 1035 specifies that labels (subdomains) should not exceed 63 octets in length. The full domain name, including all labels and separating dots, must not exceed 255 octets. These measurements are based on octets rather than characters, which is important for handling special characters and internationalized domain names.

Tip: Understanding Octets vs. Characters

An octet is 8 bits, typically equivalent to one byte. While often interchangeable with "character" in ASCII, they differ for Unicode. For example, the character "ñ" uses 2 octets in UTF-8 encoding. This distinction is crucial when working with internationalized domain names.

Subsequent RFC Updates

Several RFCs have confirmed or clarified the original specifications:

RFC 2181 (July 1997) reaffirmed the 255-octet limit for full domain names.

RFC 3986 (January 2005) advised URI producers to follow DNS syntax and limit names to 255 characters.

RFC 5321 (October 2008) maintained the 255-octet maximum for domain names but suggested a 64-character limit for labels. However, the industry standard remains at 63 characters for compatibility.

The current industry standard follows the original RFC 1035 guidelines:

  • Labels (subdomains): Maximum 63 octets
  • Full domain names: Maximum 253 octets (practical limit, accounting for email address format)

These standards help maintain consistency and compatibility across various internet systems and applications.