IP Subnet / CIDR Calculator
Enter an IPv4 address with a CIDR prefix and get the network address, broadcast, netmask and usable host range instantly — computed locally in your browser.
A CIDR block like 10.0.0.0/24 packs an IP address and a subnet mask into one notation. The prefix (/24) tells you how many bits are fixed for the network, leaving the rest for host addresses. This calculator expands that into everything you need when planning or auditing a subnet: the network address, the broadcast address, the equivalent dotted netmask and wildcard mask, and the first/last usable host in the range.
Enter any IPv4 address and prefix length (0–32) above. The math runs entirely client-side in your browser — nothing is sent to a server, so it works offline once the page has loaded and is safe to use with internal/private ranges.
Frequently asked questions
Why does a /24 have only 254 usable hosts, not 256?
The first address in the block is reserved as the network address and the last as the broadcast address, so a /24 (256 total addresses) leaves 254 assignable to hosts.
What is a wildcard mask?
It is the bitwise inverse of the netmask, used by tools like Cisco ACLs where you specify which bits are allowed to vary instead of which bits are fixed.
What about /31 and /32 networks?
A /32 identifies a single host (no network/broadcast split). A /31, per RFC 3021, is a two-address point-to-point link where both addresses are usable — this calculator handles both cases specially.