Network and broadcast addresses, usable host range, wildcard and binary masks for any IPv4 address and prefix, with correct /31 and /32 handling and a subnet split helper.
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Results
Split into smaller subnets
| Subnet | Usable hosts | Broadcast |
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How the calculator works
An IPv4 address is 32 bits. The prefix length (the number after the /) says how many of those bits identify the network; the rest identify hosts on it. A subnet mask is the same thing written as four numbers: /24 and 255.255.255.0 both mean the first 24 bits are the network.
- Network address: all host bits set to 0. It names the subnet and isn't assigned to a device.
- Broadcast address: all host bits set to 1. Traffic sent to it reaches every host on the subnet.
- Usable hosts: everything between the two, so a subnet has 2(32 − prefix) − 2 usable addresses.
- Wildcard mask: the subnet mask with every bit flipped, as used in Cisco access lists and OSPF network statements.
Example: 192.168.10.77/26
A /26 leaves 6 host bits, so each subnet holds 64 addresses: 192.168.10.0, .64, .128 and .192. The address .77 falls in the second block.
- Network address: 192.168.10.64
- Broadcast address: 192.168.10.127
- Usable hosts: 192.168.10.65 to 192.168.10.126 (62 addresses)
- Subnet mask: 255.255.255.192; wildcard mask: 0.0.0.63
/31, /32 and /0
- /31 has two addresses and, under RFC 3021, both are usable on a point-to-point link; there's no network or broadcast address. Older equipment may not support it.
- /32 is a single address, used for host routes and loopback interfaces.
- /0 is the whole IPv4 address space; in a routing table it's the default route. Its usable host count (4,294,967,294) is theoretical.
What the calculator accepts
The calculator is deliberately strict, so a typo can't quietly give you the wrong network. It rejects numbers above 255, leading zeros such as 010 (some systems read them as octal), masks whose 1 bits aren't contiguous, and stray spaces or characters. If you paste a wildcard mask where a subnet mask belongs, it tells you the subnet mask to use instead.
Address classes (A to E) are shown for reference only. Networks have been classless since CIDR (RFC 4632), so the prefix length, not the class, decides the network size.
Related reference
For a printable subnet-size table, see the IPv4 Subnetting cheat sheet by Jeremy Stretch in the PacketLife library. For how subnets fit into a small network's VLAN plan, see IP addresses and subnets in Building a Reliable Home or Small Business Network, and more networking guides under Networking & Wi-Fi.
Standards and references
For how the IT Resource Center is researched, reviewed and corrected, see How These Guides Are Made.