Subnet Calculator

A subnet is a logical slice of an IP network. The CIDR notation (Classless Inter-Domain Routing, e.g. 10.0.0.0/24) expresses how many leading bits belong to the network — the remaining bits identify hosts inside that network.

What the calculator returns

• Network address — the first IP of the block; identifies the subnet, not assignable to a host.
• Broadcast address — the last IP; reaches every host in the subnet, not assignable.
• First and last usable host — the range you can actually assign to devices.
• Netmask — decimal form of the prefix (e.g. /24 → 255.255.255.0).
• Wildcard mask — inverse of the netmask; used by ACLs (Cisco) and OSPF.
• Host count — total addresses minus 2 (network + broadcast).

FAQ

Why does a /31 have only 2 hosts and no broadcast? RFC 3021 lets point-to-point links use both IPs as hosts; the network/broadcast convention is skipped for link efficiency.

Is there anything smaller than /32? No. A /32 is a single IP — useful for loopbacks and host routes.

How do I pick a prefix size? Count the hosts you need, add headroom (30–50%), and take the next power of two: 10 hosts → /28 (14 usable), 50 hosts → /26 (62 usable).