Which port number is conventionally associated with DNS?

The Domain Name System is conventionally associated with port 53.

DNS translates human-readable names such as example.org into information used by networked computers, including IP addresses. DNS queries and replies traditionally use User Datagram Protocol on port 53 because UDP is lightweight and handles ordinary lookups efficiently.

DNS can also use Transmission Control Protocol on port 53. TCP is important for zone transfers and for responses that cannot fit conveniently into a normal UDP exchange. Modern DNS technologies can additionally use encrypted transports such as DNS over HTTPS or DNS over TLS, but the traditional DNS service is still identified with port 53.

Port numbers are not the same as protocols. Port 80 is conventionally associated with HTTP, while port 443 is associated with HTTPS. Port 53 identifies the customary DNS service endpoint, not a domain name or an IP address.