An IP subnet calculator works out the boundaries of any IPv4 network from its CIDR notation — the slash number that tells you how many bits belong to the network. Whether you're planning firewall rules, designing a VPC, or double-checking a network config, this tool gives you the network address, broadcast address, usable range, and wildcard mask (the ACL format) without having to count bits manually. The bits display at the top shows exactly which bits are network and which are host, which makes the /notation click a lot faster than any table.