IPv4 Subnet Calculator

You probably just need the network address and how many hosts fit — here's where to look

Type the IP with the prefix — 192.168.1.130/26 works, or enter them as separate fields. The result you care about is usually the network address, the broadcast, and the usable host count. Those three tell you whether your block is the right size for what you're building. The first and last usable IPs are right there too, so you can configure your DHCP start and end range without doing the arithmetic yourself. Everything else — total addresses, wildcard mask, network class — is there if you need it but it doesn't crowd the main result.

Open the binary view if you're actually learning subnetting

There's a Binary Representations section you can expand. It shows the subnet mask, network address, broadcast, and host range all written out as four 8-bit groups. If subnetting is something you learned from a book and you've never really felt confident about it, this is the part that makes it click. You can see exactly where the network portion ends and the host portion starts. The wildcard mask shown there — the bitwise inverse of the subnet mask — is the form used in Cisco ACL entries and OSPF configs, so it's handy to have it spelled out rather than having to calculate it separately.