The Subnet Calculator is a fundamental tool for network engineers, sysadmins and anyone studying for networking certifications. Enter an IPv4 address and a CIDR prefix length and the tool instantly calculates the network address, broadcast address, subnet mask, wildcard mask, first and last usable host addresses, and the total number of usable hosts in that subnet.

The visual host range bar gives an at-a-glance view of the subnet structure, showing the network address, usable host range and broadcast address in proportion. The binary subnet mask display shows exactly which bits are network bits (1s) and which are host bits (0s), which is essential for understanding how subnetting works rather than just getting the numbers.

The CIDR Quick Reference table at the bottom covers the most commonly used prefix lengths from /8 to /32 with their subnet masks, wildcard masks, total addresses and typical use cases. Click any row to calculate that prefix using your entered IP address. This is useful for quickly checking what a /27 or /29 gives you without having to do the binary arithmetic manually.