CIDR calculator
Subnet math, computed locally. Safe for internal ranges.
Network
Broadcast
First host
Last host
Usable hosts
Netmask
Wildcard
Prefix
Binary (network | host)
Subnet math, computed locally. Safe for internal ranges.
An IPv4 address is a 32-bit number; CIDR notation splits it into a network part and a host part at the prefix boundary. Everything on this page — network address, broadcast, usable range — falls out of two bitwise operations: AND with the netmask, OR with its inverse. The binary row shows the exact split, which makes off-by-one subnet bugs visible at a glance.
Edge cases are handled the way routers actually behave: /31 links have two usable addresses per RFC 3021, /32 is a single host route, and an address without a prefix is treated as /32.
The prefix length: how many leading bits of the address identify the network. A /24 fixes the first 24 bits, leaving 8 bits (256 addresses, 254 usable hosts) for machines. Bigger prefix, smaller network.
The all-zeros host address names the network itself and the all-ones address is the broadcast. Exceptions: /31 point-to-point links use both addresses (RFC 3021) and a /32 is a single host.
The bitwise inverse of the netmask — 0.0.0.255 for a /24. Cisco ACLs and some firewall rules use wildcard masks instead of netmasks to select address ranges.
No. This is 32-bit integer math running in your browser. Paste internal ranges freely — nothing leaves the page.