What is the IPv4 CIDR Subnet Calculator?
Enter an IPv4 address and a CIDR prefix and this calculator works out the network address, broadcast address, usable host range, subnet mask, and total host count.
How it works
It converts the IP address into a 32-bit integer and builds a bitmask from the CIDR prefix length, then uses bitwise AND/OR/NOT operations against that mask to derive the network address, the broadcast address, and the number of host addresses available.
SysAdmin & security use cases
- Splitting a /24 office network into smaller /27 or /28 subnets for separate VLANs.
- Checking how many usable hosts a given CIDR block actually provides before provisioning a VPC subnet.
- Verifying the broadcast address for a subnet before writing a firewall rule.
- Double-checking a colleague's proposed subnet plan for overlapping address ranges.