TOOL
Subnet Calculator
Enter an IPv4 address with a mask or CIDR prefix to see the network, broadcast, usable range, host count and binary breakdown.
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How to use it
Enter an IPv4 address and either a CIDR prefix (24 or /24) or a dotted subnet mask (255.255.255.0). The calculator shows the network address, broadcast address, first and last usable host, total and usable host counts, the mask in both forms, and the wildcard mask, with the network and host bits highlighted in binary.
What the results mean
- Network address: the first address in the block, identifying the subnet itself. Not assignable to a host.
- Broadcast address: the last address, used to reach every host on the subnet. Not assignable.
- Usable range: the addresses you can assign to devices, between those two.
- Wildcard mask: the inverse of the subnet mask, used in access control lists on some platforms.
The concepts are explained in the subnet mask and CIDR notation records. To split a block into smaller subnets or aggregate ranges, use the CIDR Calculator.
Worked example
For 10.20.30.77/27: the /27 gives 32 addresses per subnet, blocks start every 32 in the last octet, and 77 falls in the 64–95 block. The result is network 10.20.30.64, broadcast 10.20.30.95, usable 10.20.30.65–10.20.30.94, 30 usable hosts.
Frequently asked questions
How many usable hosts are in a /24?
A /24 (255.255.255.0) contains 256 addresses, of which 254 are usable for hosts; the first is the network address and the last is the broadcast address.
What is the difference between a subnet mask and a wildcard mask?
A subnet mask marks the network bits with 1s (255.255.255.0). A wildcard mask, used in some ACLs, is its inverse, marking the host bits with 1s (0.0.0.255). This calculator shows both.