IP Subnet Calculator

An IP subnet calculator works out the boundaries of a network from a single address and its mask. Enter an IPv4 address with either a CIDR prefix such as 24 or a dotted mask such as 255.255.255.0, and it returns the network address, broadcast address, usable host range and the total number of addresses in the block. It saves converting between binary and decimal by hand when you are planning address space or checking whether two machines sit on the same subnet.