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Subnet Calculator
IPv4 and IPv6 CIDR maths: network, broadcast, usable range and subnet splits.
Everything here runs entirely in your browser. Nothing you type, paste, or upload is ever sent to a server, logged, or stored.
About the Subnet Calculator
Does the CIDR arithmetic for IPv4 and IPv6: network and broadcast addresses, the usable host range, the mask in every notation, how many addresses a prefix holds, and how a block splits into smaller ones.
When you would use it
- Planning how to divide an address block between networks.
- Working out whether a particular address falls inside a given range.
- Translating between prefix length and dotted-decimal mask.
What it does not tell you
The arithmetic is exact; whether a range is usable is a question about your network, not about the maths. IPv6 has no broadcast address, and its subnets are large enough that the host count is better read as a magnitude than as a number. Everything is computed in your browser.