What is an IP subnet calculator?
A subnet calculator takes an IP address and a subnet mask (or CIDR prefix such as /24) and works out the network address, broadcast address, usable host range, and the total number of hosts the subnet can hold. It saves you from doing binary math by hand.
Enter an address like 192.168.1.10 with a prefix of /24 and the tool shows the network (192.168.1.0), broadcast (192.168.1.255), and the 254 usable addresses in between.
How subnetting works
The subnet mask splits an IP address into a network part and a host part. A /24 mask (255.255.255.0) reserves the first 24 bits for the network, leaving 8 bits for hosts, which gives 256 addresses minus 2 (network and broadcast) = 254 usable hosts.
Smaller prefixes cover more addresses (a /16 holds 65,534 hosts); larger prefixes cover fewer (a /30 holds just 2, ideal for point-to-point links). This calculator updates every value instantly as you change the prefix.