The 255.255.255.0 subnet mask.

The /24 subnet uses 255.255.255.0 as its subnet mask — meaning the first 24 bits of every address identify the network, and the remaining 8 bits identify the host within that network. That gives you 256 total addresses (254 usable on standard RFC math, after subtracting the network and broadcast addresses).

The wildcard mask — the bitwise inverse of the subnet mask — is 0.0.0.255. Wildcards are what Cisco access-control lists and OSPF area definitions use instead of subnet masks; the "1" bits mark "don't care" positions. For a /24, that leaves 8 don't-care host bits.

To find the network address for any IP in a /24 block, perform a bitwise AND between the IP and the subnet mask. To find the broadcast, OR the network address with the wildcard. Modern tools — like our subnet calculator — do this in microseconds, but the underlying mechanics are straightforward binary arithmetic.

The single most common subnet size in practice. A /24 is the classic LAN: 254 usable hosts (251 on AWS or Azure), 255.255.255.0 mask, easy to read in dotted-decimal. AWS and GCP suggest /24 as a default subnet size.

Cloud-provider quirks matter at every prefix size: AWS and Azure reserve 5 IPs per subnet, GCP reserves 4, and OCI reserves 3. So a /24 on standard RFC math gives you 254 usable hosts, but on AWS or Azure that drops to 251. The capacity-planning gap bites hardest at small prefixes (a /28 has 14 usable on paper, only 11 on AWS) but exists at every size. Our cloud-aware calculator applies the right math automatically.