IP Subnet Calculator

This free IPv4 subnet calculator works out everything about a subnet from an IP address and a prefix length (CIDR) or a subnet mask: the network address, broadcast address, wildcard mask, the first and last usable host addresses, and how many hosts the subnet can hold. It is handy for planning networks, checking firewall rules or studying for networking exams. All calculations happen locally in your browser.

IP address

CIDR prefix length (0–32)

or subnet mask

IP address
Subnet mask
Wildcard mask
CIDR notation
Network address
Broadcast address
First usable host
Last usable host
Total addresses
Usable hosts
IP in binary

Tip: for /31 point-to-point links both addresses are usable per RFC 3021; for /32 the single address is a host route. This calculator follows those conventions.