~/tools $ ./ipcalc

Subnet Calculator

Turn CIDR notation into network, broadcast, usable host range, mask, and host count.

Runs entirely in your browser. Nothing you paste is sent anywhere.

Scope is everything

Before a single packet leaves your machine, confirm that the range you are about to scan matches the range in your rules of engagement. A typo of one bit in a prefix can double your target list, or put a stranger's network in it.

Quick reference

  • /24 is 254 usable hosts, /16 is 65,534, /8 is about 16.7 million.
  • /31 links have two usable addresses and no broadcast (RFC 3021). /32 is a single host.
  • VirtualBox host-only networks default to 192.168.56.0/24, which makes a tidy isolated lab.