CIDR / Subnet Calculator
Network, broadcast, host range, and masks from any IPv4 CIDR block.
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Common use cases
- Sizing a VPC or VLAN — checking how many hosts a /22 actually gives you
- Writing firewall or ACL rules that need the wildcard mask
- Splitting an office network into per-floor subnets without overlap
- Decoding a CIDR block in a cloud console or a colleague's network diagram
- Teaching or learning subnetting with the binary view as the ground truth
Why CIDR / Subnet Calculator?
Subnetting is pure bit arithmetic, and doing it in your head under pressure is how overlapping ranges ship to production. This calculator shows the answer and the binary working — where the prefix boundary falls, why a /24 has 254 usable hosts rather than 256, and it handles the modern edge cases (RFC 3021 /31 point-to-point links) that older calculators get wrong. It runs offline once loaded, which is occasionally exactly what you need when the network you are debugging is the one you are on.
CIDR / Subnet Calculator keeps the job narrow: network, broadcast, host range, and masks from any ipv4 cidr block. It is built for the small but frequent moments when opening a heavyweight editor, installing a package, or uploading sensitive work to a random service is more friction than the task deserves.