CIDR / Subnet Calculator

Enter an address in CIDR notation. If you enter a host address rather than the network address (e.g. 192.168.1.100/24 instead of 192.168.1.0/24), it's normalized to the correct network automatically. Runs entirely in your browser.

A note on /31 and /32

Normally a subnet reserves its first address (network) and last address (broadcast), leaving the rest usable. Two exceptions: a /31 has no room for either, so RFC 3021 allows both of its two addresses to be used as a point-to-point link. A /32 is a single address with no concept of network/broadcast at all — used for host routes.