Subnet Calculator
Network address, broadcast address, subnet mask, and usable host range for any IPv4 CIDR block.
Every calculation runs locally in your browser. Nothing you enter here is sent to a server.
Usable hosts
254
Total addresses
256
For informational and educational purposes only — not professional or technical advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
What the CIDR prefix actually controls
The number after the slash is how many leading bits of the 32-bit address are fixed as the network portion — the rest identify hosts within it. A /24 fixes the first 24 bits, leaving 8 bits (256 addresses) for hosts; a /30 leaves just 2 bits (4 addresses), typical for a point-to-point link. The first address in a block identifies the network itself and the last is reserved for broadcast, which is why usable hosts is always the block size minus 2 — except at /31 and /32, which are edge cases with no separate broadcast address under the classic convention used here.
Frequently asked questions
What does CIDR notation like /24 actually mean?
The number after the slash is how many bits of the 32-bit IPv4 address are fixed as the network portion — /24 means the first 24 bits are the network, leaving 8 bits (256 addresses, 254 usable) for hosts.
Why are two addresses in a subnet unusable for hosts?
The first address in a subnet is reserved as the network address (identifies the subnet itself) and the last is reserved as the broadcast address (sends to every host on the subnet) — neither can be assigned to an individual device.