CIDR Calculator

Calculate the network address, broadcast, usable host range and total host count for any IPv4 or IPv6 CIDR block.

About this tool

CIDR (Classless Inter-Domain Routing) notation expresses a block of IP addresses as a base address plus a prefix length — the number of bits that make up the fixed "network" portion. This calculator works out everything derived from that: the network address itself, the broadcast address (IPv4 only — IPv6 has no broadcast concept), the usable host range, and the total address count.

Notes on the edge cases

  • /31 networks (IPv4) follow RFC 3021: both addresses are usable point-to-point links, with no network or broadcast address reserved.
  • /32 is a single host — the network, broadcast, and usable address are all the same one address.
  • IPv6 host counts can be astronomically large (a single /64, the standard subnet size, contains over 18 quintillion addresses) — shown as an exact number, not an approximation.

Related tools:

IPv4 Lookup IPv6 Lookup IP Lookup