About Subnet Calculator
Usable hosts always come to two below the total: the first address names the network and the last is the broadcast address, and neither can be assigned. That arithmetic is why a /30 yields only two usable addresses.
Enter an IPv4 address and CIDR prefix to get the network and broadcast address, usable host range, host count, netmask and wildcard, then split it into subnets. All the bitwise maths runs in your browser.
A subnet calculator turns an IPv4 address and its CIDR prefix (or netmask) into everything you need to plan or troubleshoot a network: the network and broadcast addresses, the first and last usable host, the total and usable host counts, the wildcard mask and the address class. Enter something like 192.168.1.10/24 — or a netmask such as 255.255.255.0 — and every value updates instantly.
It also splits a block into equal subnets, which is the core of VLSM (variable-length subnet masking) design. Slide to a longer prefix to see how a /24 divides into /26s or /30s, complete with each child network's usable range and broadcast address.