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Subnet Calculator

IPv4 subnet details — network, broadcast, host range, and more.

Enter an IPv4 CIDR block (e.g. 10.0.0.0/8) or an IP with mask (e.g. 192.168.1.1/255.255.255.0).

Work out a subnet in one step

Enter a block in CIDR notation (192.168.1.0/24, 10.0.0.0/8) or an address with a dotted-decimal mask (192.168.1.1/255.255.255.0) and get the whole picture:

Network and broadcast addresses — the first and last address in the block.
First and last usable host — what you can actually assign to a machine.
Subnet mask, wildcard mask (for ACLs) and the mask in binary.
Total and usable host counts, the classful class, and whether the block is private under RFC 1918.

Quick reference

A /24 holds 256 addresses and 254 usable hosts; a /25 holds 128 and 126; each extra bit of prefix halves the block. A /31 is the special two-address point-to-point case from RFC 3021, and a /32 is a single host.

All arithmetic happens in your browser — no address you type is sent anywhere.