Free tool
Subnet calculator
Enter an IPv4 address and a CIDR (or dotted-decimal mask) to instantly compute network address, broadcast, usable host range, total hosts, wildcard mask, and address class. Useful when sizing VLANs, planning DHCP scopes, or reading firewall ACLs.
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Subnetting FAQ
What is a subnet mask?
A subnet mask is a 32-bit value that divides an IPv4 address into a network portion and a host portion. The contiguous 1-bits at the start indicate the network; the 0-bits indicate hosts. A /24 mask (255.255.255.0) leaves 8 bits for hosts, allowing 254 usable addresses per subnet (256 minus network and broadcast).
How do I choose between /24 and /23?
Use /24 (254 hosts) when each VLAN has at most a few hundred endpoints — typical for staff, servers, or IoT segments. Step up to /23 (510 hosts) when you genuinely need more addresses; never oversize for vanity. A poorly sized subnet wastes address space and complicates broadcast traffic. As a rule of thumb, target ≤ 60% utilization at peak so you have headroom for growth.
Why does my calculator say 254 usable hosts on /24, not 256?
The first address in any subnet is the network address (e.g., 192.168.1.0) and the last is the broadcast address (192.168.1.255). Neither can be assigned to a host, so a /24 yields 256 − 2 = 254 usable addresses. /31 and /32 are special cases used for point-to-point links and loopback assignments respectively.
What's the difference between a subnet mask and a wildcard mask?
A subnet mask flags the network bits as 1s (e.g., 255.255.255.0). A wildcard mask is its bitwise inverse (0.0.0.255) and is most often used in Cisco IOS ACLs and OSPF area definitions to specify which bits the device should ignore when matching. ZeroConf's generators emit the right form for each vendor automatically.