Per-Label Limit
Each segment between dots (called a “label”) can contain up to 63 characters. Labels may include letters, digits, and hyphens, but cannot begin or end with a hyphen. For internationalized domain names (IDNs), any Unicode characters are converted into ASCII (punycode), and that punycode string counts toward the 63-character limit.
Overall Length
The entire domain name—including every label, each dot separator, and the optional trailing dot—cannot exceed 253 characters when transmitted over the DNS protocol (255 if you include the final dot). Most registries enforce this 253-character cap. For instance, a single 63-character label such as
“this-is-a-63-character-label-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx”
followed by “.com” still keeps the total under 253 characters.
Why These Limits Exist
These constraints come from the original DNS specifications (RFC 1035 and RFC 3696). They ensure that DNS packets remain small enough to traverse networks without fragmentation, keep lookups fast, and maintain compatibility across all DNS servers worldwide.
Best Practices
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Use concise labels: Aim for meaningful words under 20 characters to improve memorability and avoid typos.
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Avoid too many subdomains: Each extra label eats into the 253-character budget.
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Watch IDN conversions: Punycode can expand a short Unicode name into a much longer ASCII string. Test conversion before registering.
