CIDR Calculator
Enter an IPv4 address (as four octets) and a CIDR prefix length to see the subnet mask, network range, and number of usable hosts.
What CIDR notation means
CIDR (Classless Inter-Domain Routing) notation writes an IP network as an address followed by a slash and a prefix length, like 192.168.1.0/24. The prefix length tells you how many leading bits of the address are fixed as the network portion, with the rest available for host addresses.
How this calculator works
Enter your IP address as four separate octets and a prefix length. The calculator combines the octets into a single 32-bit number, builds a subnet mask from the prefix length by setting that many leading bits to 1, and applies the mask to find the network address. The broadcast address is the network address with all host bits set to 1. The number of usable host addresses is 2 raised to the power of the remaining host bits, minus 2 for the reserved network and broadcast addresses (except for /31 and /32 networks, which use special rules).
This tool is for general networking reference and planning purposes.