Subnet and PortsWhat is here
Seven calculators, four reference tables and a port guide, all running in your browser. Nothing you type is sent anywhere.
| You want to... | Use |
|---|---|
| Find the network, broadcast and host range of an address | IPv4 subnet calculator |
| Split a network into smaller ones | Subnet splitter |
| Turn /24 into 255.255.255.0 or back | Subnet mask converter |
| Turn a range of addresses into CIDR blocks | IP range to CIDR |
| See the first and last address of a block | CIDR to IP range |
| Test whether an address belongs to a block | Is this IP in this subnet |
| Shorten an IPv6 address or find its range | IPv6 subnet calculator |
| Look up what a port number is used for | Port numbers |
How to learn subnetting
Start with "What is subnetting", then "How to subnet step by step", and practise with the calculator: work out the answer by hand first, then type the address to check. The cheat sheet of prefixes from /8 to /32 is worth keeping beside you.
Frequently asked questions
Are the calculators accurate?
We compared them with Python's ipaddress module on 1,400 random cases and found no differences.
Does the site store the addresses I type?
No. The calculators run in your browser. The address in the page's link is only there so that you can share a result.
Why do some ports show several registered names?
The IANA registry sometimes lists more than one service for the same number. The pages show all of them.
This is an independent guide. It is not connected with IANA, the IETF or any network equipment maker. Address and port data come from the IANA registries as fetched on 14 November 2026; RFC texts were read from rfc-editor.org. Check the originals for anything you rely on.