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Subnet Calculator

Calculate network, broadcast, host range and split any CIDR block.

Processed locally — nothing is uploaded

About Subnet Calculator

Usable hosts always come to two below the total: the first address names the network and the last is the broadcast address, and neither can be assigned. That arithmetic is why a /30 yields only two usable addresses.

A subnet calculator turns an IPv4 address and its CIDR prefix (or netmask) into everything you need to plan or troubleshoot a network: the network and broadcast addresses, the first and last usable host, the total and usable host counts, the wildcard mask and the address class. Enter something like 192.168.1.10/24 — or a netmask such as 255.255.255.0 — and every value updates instantly.

It also splits a block into equal subnets, which is the core of VLSM (variable-length subnet masking) design. Slide to a longer prefix to see how a /24 divides into /26s or /30s, complete with each child network's usable range and broadcast address.

Learn how this works

Understanding Your IP Address & Network BasicsWhat your public IP reveals, how to check it, and what latency means — explained simply, with a free in-browser network tester.6 min read

Frequently asked questions

Is my network data sent anywhere?

No. Everything runs locally in your browser using standard web APIs — your text, files and inputs are never uploaded to a server, so the tool works even offline once the page has loaded.

What is the difference between total and usable hosts?

Total addresses include the network and broadcast addresses, which cannot be assigned to hosts. Usable hosts subtract those two — except for /31 (a point-to-point link with 2 usable addresses per RFC 3021) and /32 (a single host). In a typical /24 network (192.168.1.0/24), you have 256 total addresses, but only 254 are usable for actual devices (subtracting .0 for network and .255 for broadcast). Understanding this distinction is critical for network planning, ensuring you allocate subnets large enough to accommodate all the devices you need while accounting for overhead.

Can I enter a netmask instead of a CIDR prefix?

Yes. You can type 10.0.0.5/24, 10.0.0.5 255.255.255.0, or a bare IP (which is treated as /32). The calculator accepts all three.

More Subnet Calculator tools

IPv4 Subnet CalculatorCIDR to Subnet Mask Converter

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