192.168.1.0/24).CIDR (Classless Inter-Domain Routing) notation describes an IP network as an address and a prefix length — /24 means the first 24 bits identify the network and the remaining 8 bits are for hosts. This calculator works out all derived values: subnet mask, network/broadcast addresses, host range, and usable host count — essential for firewall rules, cloud VPC configuration, and network design.
A /32 is a single host. /30 gives 4 addresses (2 usable) — the smallest practical point-to-point subnet. /24 gives 256 addresses (254 usable hosts) — the classic class C. /16 gives 65,536 addresses — class B. /8 gives 16,777,216 — class A. The usable hosts formula is 2^(32−prefix) − 2, subtracting the network and broadcast addresses. Note: cloud providers (AWS, GCP, Azure) typically reserve 5 addresses per subnet, reducing usable hosts further.
255.255.255.0 — the first 24 bits are all 1s (11111111.11111111.11111111.00000000), covering the first three octets.
The first address (all host bits = 0) is the network address, used to identify the subnet itself. The last address (all host bits = 1) is the broadcast address. Neither can be assigned to a host.
A wildcard mask is the bitwise inverse of a subnet mask. Where a subnet mask has 1s (network bits), the wildcard mask has 0s, and vice versa. Used in Cisco ACLs and routing protocols to specify which bits must match.
Apply the subnet mask (bitwise AND) to both addresses. If the results are equal, they are in the same subnet. For example, 192.168.1.50 AND 255.255.255.0 = 192.168.1.0; 192.168.1.200 AND 255.255.255.0 = 192.168.1.0 — same network.
See also the Binary to IP converter and IP Lookup tool for network work.