CIDR / Subnet Calculator

An IPv4 CIDR and subnet calculator. Enter an address with a prefix or subnet mask and get the network address, broadcast address, subnet and wildcard masks, usable host range, total address count, and binary representation — all computed locally.

What input formats does it accept?

CIDR notation (192.168.1.10/24), an IP address plus a dotted subnet mask (192.168.1.10 255.255.255.0), or a bare IP address (treated as a /32, a single host).

Why do /31 and /32 show different usable host counts than the normal formula?

The usual "total addresses minus 2" rule assumes a separate network and broadcast address. A /32 is a single address with no separate network/broadcast, so it has 1 usable host. A /31 is a point-to-point link (RFC 3021) where both addresses are usable with no broadcast address reserved, so it has 2.

What is the wildcard mask, and how is it different from the subnet mask?

The wildcard mask is the bitwise inverse of the subnet mask — it's the format Cisco access control lists and OSPF configuration expect instead of a regular subnet mask (e.g. 0.0.0.255 instead of 255.255.255.0 for a /24).

Is this only for IPv4?

Yes, currently only IPv4 — IPv6 prefix calculations work differently and aren't covered here.