IPv4 Subnet Calculator

Splitting a network into smaller blocks, checking whether two IPs share a subnet or sizing how many hosts fit in a /26 all require converting addresses to binary and applying a mask, and doing that in your head is how mistakes happen. Type the IP with its CIDR prefix (e.g. 192.168.1.64/26) and get the network address, broadcast, first and last host, usable host count, subnet mask and the binary breakdown all at once.

A /n prefix yields 2 to the power of (32-n) addresses, minus 2 usable hosts, because the first address names the network and the last one is the broadcast. The exception many calculators ignore: on a /31, used for point-to-point links (RFC 3021), both addresses are usable, and /32 means a single host; this tool handles both correctly. It also shows the wildcard mask (the inverse), which is the format Cisco ACLs and OSPF configuration expect.

The binary view is the fastest way to see why 192.168.1.64/26 runs from .64 to .127: the first 26 bits stay fixed and the remaining 6 vary. Try the built-in examples (/8, /16, /24, /26, /30) to build intuition for block sizes. IPv4 only: IPv6 prefix logic is different and there is no broadcast address there. Everything is computed in your browser, and no address you type is sent to any server.