Subnet Calculator
Subnet Calculator
Enter an IPv4 address and choose a prefix length (CIDR) to calculate the full subnet details.
The Subnet Calculator works out everything about an IPv4 subnet from just an address and a prefix length: the network address, broadcast address, netmask, wildcard mask, first and last usable hosts, and exactly how many addresses and hosts the subnet contains. Network planning, firewall rules, and troubleshooting all start with these numbers, and doing the binary arithmetic by hand is slow and famously error-prone.
Choose any prefix from /8 to /32, covering everything from large private ranges down to a single-host route. The calculator handles the special cases honestly too: /31 point-to-point links and /32 host routes have no spare network and broadcast addresses, so the usable host count reflects real practice instead of the textbook formula that would report a negative or meaningless number.
The wildcard mask is included because router access-lists, especially on Cisco-style equipment, ask for the inverse of the netmask. All calculations use exact integer maths in your browser; nothing is uploaded, so internal network details stay internal.
How to use
- Type an IPv4 address, for example 192.168.1.10.
- Choose the prefix length (CIDR) for your subnet.
- Click Calculate.
- Read the network, broadcast, host range, and counts in the table.
Frequently asked questions
Why are two addresses subtracted for usable hosts?
In a normal subnet the first address names the network itself and the last is the broadcast address, so neither can be given to a device. The exceptions are /31 links and /32 routes, which this calculator flags with zero usable hosts under the classic rule.
What is a wildcard mask?
It is the bitwise inverse of the netmask: where the netmask has 1s the wildcard has 0s and vice versa. Router ACLs and some routing protocols use it to say which address bits must match.
What does /24 mean in plain words?
The first 24 bits identify the network, leaving 8 bits for hosts: 256 addresses in total, 254 usable for devices in the classic layout.
Are my network details uploaded?
No. The calculation runs entirely in your browser.