Subnet Calculator
CIDR in โ mask, network, broadcast, host range and counts out.
About this calculator
Type 192.168.1.0/24 โ or an address plus mask โ and read the whole subnet: network and broadcast addresses, subnet and wildcard masks, first and last usable hosts, address counts, and whether the block is private, loopback or public. Every row copies on click; everything is computed locally from bit arithmetic, no lookups.
CIDR in one paragraph
The /N counts how many leading bits name the network; the remaining 32โN bits name hosts within it. So /24 leaves 8 host bits โ 256 addresses, minus the network address and broadcast โ 254 usable; every step of N halves or doubles the block. The special cases handled honestly: /31 point-to-point links use both addresses (RFC 3021 โ no broadcast needed between two routers), and /32 is a single host. The private ranges worth recognising on sight โ 10/8, 172.16/12, 192.168/16 โ are RFC 1918 space, which is why every home router lives at 192.168-something. The wildcard mask (the mask inverted) is what Cisco ACLs want, hence its row. The binary story underneath is its own guide, and the base converter turns any octet into bits on demand.
Frequently asked questions
How many usable hosts in a /24?
254 โ the 8 host bits give 256 addresses, minus the network (.0) and broadcast (.255). Each smaller prefix doubles it: /23 has 510, /25 has 126.
What's the difference between /24 and 255.255.255.0?
None โ they're the same mask written as a prefix length versus dotted decimal. The calculator accepts either form.
Why does a /31 show two usable hosts?
RFC 3021: point-to-point links between routers don't need a broadcast address, so both addresses of a /31 are usable. Traditional subnetting rules only apply from /30 up.
Which addresses are private?
The RFC 1918 blocks โ 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 โ plus 127/8 loopback and 169.254/16 link-local. The calculator labels what you type.